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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Brake light fuse blows intermittently
My daughters 97 Avalon blows the brake light fuse about every other day.
I thought I'd eliminate some wiring as a troubleshooting procedure. There is a connector block on the side next to the drivers foot. I found the brake light wire at the connector and in the trunk. I cut the wire at the connector and ran a new wire from the front to the trunk, I also cut the wire in the trunk, and wired the new wire to the brake lights. That leaves just a short old wire in the trunk going to both the left and the right brake light. The fuse opened again a couple days later. Is there anything internal to the brake lights that could short to cause the fuse to blow? There is at least one other circuit run by that fuse, there is a shift lever release (solenoid?) mechanism. You must push the brake pedal to move the shift lever. Any help? Thanks, Mikek |
#2
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Brake light fuse blows intermittently
amdx wrote:
My daughters 97 Avalon blows the brake light fuse about every other day. I thought I'd eliminate some wiring as a troubleshooting procedure. There is a connector block on the side next to the drivers foot. I found the brake light wire at the connector and in the trunk. I cut the wire at the connector and ran a new wire from the front to the trunk, I also cut the wire in the trunk, and wired the new wire to the brake lights. That leaves just a short old wire in the trunk going to both the left and the right brake light. The fuse opened again a couple days later. Is there anything internal to the brake lights that could short to cause the fuse to blow? There is at least one other circuit run by that fuse, there is a shift lever release (solenoid?) mechanism. You must push the brake pedal to move the shift lever. Any help? Thanks, Mikek Very possible the wires have chafed around the solenoid, it does move a little when operated, it's possible the wire harness is moving with it. It's also possible the solenoid has come loose and moving excessively, which in turn will move the wires. And there is also the other possibility, if the solenoid is under the car, outside, you may have rot or varmint eaters. I would put a tail light bulb inseries with the fuse or use it as a fuse and start moving some wires around when the brake is applied, and move the shifter etc.. watch for sudden bright glow.. That'll save fuses. Jamie |
#3
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Brake light fuse blows intermittently
On 5/12/2013 7:12 PM, Jamie wrote:
amdx wrote: My daughters 97 Avalon blows the brake light fuse about every other day. I thought I'd eliminate some wiring as a troubleshooting procedure. There is a connector block on the side next to the drivers foot. I found the brake light wire at the connector and in the trunk. I cut the wire at the connector and ran a new wire from the front to the trunk, I also cut the wire in the trunk, and wired the new wire to the brake lights. That leaves just a short old wire in the trunk going to both the left and the right brake light. The fuse opened again a couple days later. Is there anything internal to the brake lights that could short to cause the fuse to blow? There is at least one other circuit run by that fuse, there is a shift lever release (solenoid?) mechanism. You must push the brake pedal to move the shift lever. Any help? Thanks, Mikek Very possible the wires have chafed around the solenoid, it does move a little when operated, it's possible the wire harness is moving with it. It's also possible the solenoid has come loose and moving excessively, which in turn will move the wires. And there is also the other possibility, if the solenoid is under the car, outside, you may have rot or varmint eaters. I would put a tail light bulb inseries with the fuse or use it as a fuse and start moving some wires around when the brake is applied, and move the shifter etc.. watch for sudden bright glow.. That'll save fuses. Jamie Thanks Jamie, Good suggestions the solenoid and series bulb. I'll have to figure out the Shifter release, no clue how that operates. Everything is so tight, I don't like working under the dash. My wife's relative usually does my repair work, but he got in a little huf when he said he new how to fix it and I quizzed him on why "THAT" part would short to ground. I backed off and let him do what he does. He replaced the part and it still blows fuses, I didn't tell him his repair failed, because generally I'm happy to have him fix most of my auto problems. Anyway next time my daughter comes to town, I'll try your suggestions. Hmm, while I'm waiting I think I'll look into a resettable circuit breaker. Mikek PS, I do like the fact that when the brake light fuse blows, the shift lever won't move. It gives you notice! However my daughter was creative enough to find the mechanical release and drive anyway. I didn't think much about it when she told me, until I had a random thought, "I wonder if her brake lights work. That's when she started supporting the fuse company. |
#4
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Brake light fuse blows intermittently
Is the fuse the right size?
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#5
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Brake light fuse blows intermittently
amdx wrote:
My daughters 97 Avalon blows the brake light fuse about every other day. Googling finds wiring diagrams at http://autolib.diakom.ru/CAR/Toyota/...RAMS/12053.pdf and http://autolib.diakom.ru/CAR/Toyota/...RAMS/12078.pdf ; not sure if those are exactly the right ones for your car but maybe they help. There are more at http://autolib.diakom.ru/CAR/Toyota/...NG%20DIAGRAMS/ .. Both diagrams show that the stop fuse should be 10 A. There should also be a sticker inside the fuse box (or lid of the fuse box) with the correct fuse ratings. General advice: In my experience, the problem is more likely to be in a switch, lamp socket, or connector, rather than the wire itself. If it *is* in the wire, it's often near the end of the wire (where it is more exposed to moving parts, humans, etc) rather than buried in the middle of the harness somewhere. Is there anything internal to the brake lights that could short to cause the fuse to blow? If the lamp socket is really mangled, it's possible for the "hot" contact to touch the "ground" contact. You can usually tell by taking out the lamp and looking down into the socket. It's even possible, but really rare, for something to be rattling around inside the bulb (like a piece of a filament support), but I mention it because it's usually really easy to check - just take out the lamp, hold it up to the light, turn it this way and that and maybe thump it with your fingers. You might check the lamps to make sure that the right part number is in there. The owner's manual and/or website of the friendly local auto parts store should help. It should be relatively difficult for somebody to install lamps of such high power that they blow the fuse, but it's pretty simple to check. A single rear brake lamp should draw about 2 to 2.5 A depending on the exact part number. The third brake lamp will be less than this, probably closer to 1 A. This gives a minimum of about 5 to 6 A; if somebody has installed a 5 A fuse for the brake lights, you have just found the problem. Some rear lamp clusters have a short harness (like 8 inches or 20 cm) that goes from all of the lamp sockets on the cluster to a single connector with maybe 6 pins; this is for ease of assembly and replacement. Often this harness is zip-tied or otherwise fastened to the back of the cluster; maybe the zip tie cut the wires and shorted the brake light wire to ground. Sometimes cargo in the trunk can cut the rear light wires, especially if the trunk lining is gone or out of place. If this car has or ever had a trailer hitch on it, check the trailer wiring, or the remains of it. Often this is not properly routed and sometimes get pinched against the body. Or, if it had a hitch that was later removed, sometimes people just let the wires dangle down behind the rear bumper. If it doesn't have a hitch now, get a good light and look under the back of the car, towards the bumper, for non- factory-looking holes, or cuts in the bumper cover, where a hitch might have gone. Also look at the rear lamp clusters from the trunk to see if there are any non-factory-looking splices. Check the third brake light as well; it's on the same circuit. Usually its wire runs on the bottom side of the rear parcel shelf, in the trunk, from the light over to one side of the car. The owner's manual should tell you how to get the lamp out of it, which will let you inspect the lamp and socket. You might look at the brake light switch, which is mounted to a bracket near the brake pedal arm; it's above your toes if you're stepping on the brake. Usually it's not too hard to at least get your eyeballs on it, even if working on it is more entertaining. Usually when these fail, the plastic switch body cracks and the brake lights just stop working. Sometimes the driver catches the wires to the brake light switch with the toe of his or her shoe and pulls them around, which might make them short out on the brake light switch bracket or other nearby metal. The wiring diagram linked above shows a "light failure fixture" which lives on the left rear lamp cluster. This monitors the current to the brake and tail lights and turns on a "lamp failed" indicator on the dash if anything isn't drawing enough current. This could conceivably be screwing up and shorting the brake light wire to ground. If it's not obviously mechanically beat up, I would assume it's OK on the first pass. If you start to suspect it, the test is probably to bypass it and see if it stops blowing fuses. The bypass would be to unplug it and splice the green-white (brake feed), green-red (regular brake lights), and green-orange (third brake light) wires together; and separately splice the green (tail feed) and light green (tail lights) wires together. The other three wires can be left open. If you bypass it, the "lamp failed" indicator on the dash won't work anymore. There is at least one other circuit run by that fuse, there is a shift lever release (solenoid?) mechanism. This is a solenoid that usually lives somewhere near the bottom of the shift lever. You may be able to hear it "thunk" if you put your ear by the shift lever while pushing on the brake pedal. The wiring diagram above shows that there is a shift lock ECU that has a wire from the brake light switch, as well as direct wires from two other fuses. I think the brake light signal is probably an input to the shift lock ECU, rather than a power source for it, but a short on the brake light signal wire would still blow the brake light fuse. If the car has a console shift, sometimes coins, soda, etc falls in around the shift lever; usually it just makes a mess but something metal might eventually wear through a wire. I hope this helps! Matt Roberds |
#6
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Brake light fuse blows intermittently
On 5/12/2013 7:55 PM, William Sommerwerck wrote:
Is the fuse the right size? Yes, it is. Mikek |
#8
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Brake light fuse blows intermittently
amdx wrote:
On 5/12/2013 7:12 PM, Jamie wrote: amdx wrote: My daughters 97 Avalon blows the brake light fuse about every other day. I thought I'd eliminate some wiring as a troubleshooting procedure. There is a connector block on the side next to the drivers foot. I found the brake light wire at the connector and in the trunk. I cut the wire at the connector and ran a new wire from the front to the trunk, I also cut the wire in the trunk, and wired the new wire to the brake lights. That leaves just a short old wire in the trunk going to both the left and the right brake light. The fuse opened again a couple days later. Is there anything internal to the brake lights that could short to cause the fuse to blow? There is at least one other circuit run by that fuse, there is a shift lever release (solenoid?) mechanism. You must push the brake pedal to move the shift lever. Any help? Thanks, Mikek Very possible the wires have chafed around the solenoid, it does move a little when operated, it's possible the wire harness is moving with it. It's also possible the solenoid has come loose and moving excessively, which in turn will move the wires. And there is also the other possibility, if the solenoid is under the car, outside, you may have rot or varmint eaters. I would put a tail light bulb inseries with the fuse or use it as a fuse and start moving some wires around when the brake is applied, and move the shifter etc.. watch for sudden bright glow.. That'll save fuses. Jamie Thanks Jamie, Good suggestions the solenoid and series bulb. I'll have to figure out the Shifter release, no clue how that operates. Everything is so tight, I don't like working under the dash. My wife's relative usually does my repair work, but he got in a little huf when he said he new how to fix it and I quizzed him on why "THAT" part would short to ground. I backed off and let him do what he does. He replaced the part and it still blows fuses, I didn't tell him his repair failed, because generally I'm happy to have him fix most of my auto problems. Anyway next time my daughter comes to town, I'll try your suggestions. Hmm, while I'm waiting I think I'll look into a resettable circuit breaker. Mikek PS, I do like the fact that when the brake light fuse blows, the shift lever won't move. It gives you notice! However my daughter was creative enough to find the mechanical release and drive anyway. I didn't think much about it when she told me, until I had a random thought, "I wonder if her brake lights work. That's when she started supporting the fuse company. my 2011 Jeep Cherokee had an addendum in the glove on how to release the shift lock, you need to move the rubber that goes around the shift and you are suppose to be able to reach the solenoid actuator so you can release it. Jamie |
#9
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Brake light fuse blows intermittently
William Sommerwerck wrote:
Is the fuse the right size? good question, could also be a slow blow type. Jamie |
#10
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Brake light fuse blows intermittently
amdx wrote:
On 5/13/2013 1:44 AM, wrote: amdx wrote: My daughters 97 Avalon blows the brake light fuse about every other day. Googling finds wiring diagrams at http://autolib.diakom.ru/CAR/Toyota/...RAMS/12053.pdf and http://autolib.diakom.ru/CAR/Toyota/...RAMS/12078.pdf ; not sure if those are exactly the right ones for your car but maybe they help. Very helpful, The first diagram let me learn that I have bypassed the "light failure fixture" with my new wire. The "light failure fixture" had been replaced by the relative that said he knew how to repair the problem (he didn't). There are more at http://autolib.diakom.ru/CAR/Toyota/...NG%20DIAGRAMS/ . Both diagrams show that the stop fuse should be 10 A. There should also be a sticker inside the fuse box (or lid of the fuse box) with the correct fuse ratings. Yes, 10 amp fuse, and I warned my daughter to replace it only with another 10 amp fuse. General advice: In my experience, the problem is more likely to be in a switch, lamp socket, or connector, rather than the wire itself. If it *is* in the wire, it's often near the end of the wire (where it is more exposed to moving parts, humans, etc) rather than buried in the middle of the harness somewhere. My wire replacement seems to confirm your experience :-) Is there anything internal to the brake lights that could short to cause the fuse to blow? If the lamp socket is really mangled, it's possible for the "hot" contact to touch the "ground" contact. You can usually tell by taking out the lamp and looking down into the socket. Nothing has been damaged externally, next check I'll open up the rear lights and check their condition. It's even possible, but really rare, for something to be rattling around inside the bulb (like a piece of a filament support), but I mention it because it's usually really easy to check - just take out the lamp, hold it up to the light, turn it this way and that and maybe thump it with your fingers. I'll include that in my inspection. You might check the lamps to make sure that the right part number is in there. The owner's manual and/or website of the friendly local auto parts store should help. It should be relatively difficult for somebody to install lamps of such high power that they blow the fuse, but it's pretty simple to check. I'll keep that in mind, I got no feedback that any lamps had been replaced, but one should not assume, especially with a problem that is intermittent. A single rear brake lamp should draw about 2 to 2.5 A depending on the exact part number. The third brake lamp will be less than this, probably closer to 1 A. This gives a minimum of about 5 to 6 A; if somebody has installed a 5 A fuse for the brake lights, you have just found the problem. That's not the situation. Some rear lamp clusters have a short harness (like 8 inches or 20 cm) that goes from all of the lamp sockets on the cluster to a single connector with maybe 6 pins; this is for ease of assembly and replacement. Often this harness is zip-tied or otherwise fastened to the back of the cluster; maybe the zip tie cut the wires and shorted the brake light wire to ground. That's where I started, inspecting the wiring in the trunk, even opened the spiral wrap looking for damage. No damage found. Sometimes cargo in the trunk can cut the rear light wires, especially if the trunk lining is gone or out of place. If this car has or ever had a trailer hitch on it, check the trailer wiring, or the remains of it. Often this is not properly routed and sometimes get pinched against the body. Or, if it had a hitch that was later removed, sometimes people just let the wires dangle down behind the rear bumper. If it doesn't have a hitch now, get a good light and look under the back of the car, towards the bumper, for non- factory-looking holes, or cuts in the bumper cover, where a hitch might have gone. Also look at the rear lamp clusters from the trunk to see if there are any non-factory-looking splices. No trailer hitch ever. Check the third brake light as well; it's on the same circuit. Usually its wire runs on the bottom side of the rear parcel shelf, in the trunk, from the light over to one side of the car. The owner's manual should tell you how to get the lamp out of it, which will let you inspect the lamp and socket. Already disassembled the third brake light assembly, also ran a new wire. You might look at the brake light switch, which is mounted to a bracket near the brake pedal arm; it's above your toes if you're stepping on the brake. Usually it's not too hard to at least get your eyeballs on it, even if working on it is more entertaining. Usually when these fail, the plastic switch body cracks and the brake lights just stop working. Sometimes the driver catches the wires to the brake light switch with the toe of his or her shoe and pulls them around, which might make them short out on the brake light switch bracket or other nearby metal. I'd rather work on the easy stuff! Oh just kidding, I have climbed under the dash and looked over the switch, didn't notice any problems. But I'm sure I'll be under there again. The wiring diagram linked above shows a "light failure fixture" which lives on the left rear lamp cluster. This monitors the current to the brake and tail lights and turns on a "lamp failed" indicator on the dash if anything isn't drawing enough current. This could conceivably be screwing up and shorting the brake light wire to ground. If it's not obviously mechanically beat up, I would assume it's OK on the first pass. If you start to suspect it, the test is probably to bypass it and see if it stops blowing fuses. The bypass would be to unplug it and splice the green-white (brake feed), green-red (regular brake lights), and green-orange (third brake light) wires together; and separately splice the green (tail feed) and light green (tail lights) wires together. The other three wires can be left open. If you bypass it, the "lamp failed" indicator on the dash won't work anymore. As I said before the "light Failure Fixture" has been replace and didn't solve the problem. I have also bypassed it. There is at least one other circuit run by that fuse, there is a shift lever release (solenoid?) mechanism. This is a solenoid that usually lives somewhere near the bottom of the shift lever. You may be able to hear it "thunk" if you put your ear by the shift lever while pushing on the brake pedal. The wiring diagram above shows that there is a shift lock ECU that has a wire from the brake light switch, as well as direct wires from two other fuses. I think the brake light signal is probably an input to the shift lock ECU, rather than a power source for it, but a short on the brake light signal wire would still blow the brake light fuse. If the car has a console shift, sometimes coins, soda, etc falls in around the shift lever; usually it just makes a mess but something metal might eventually wear through a wire. Ideally I would like to separate the two circuits as close to the fuse as possible. She can drive the car when the Shift Lever solenoid is not functioning. Then if the fuse still blows I have eliminated the the Shift Lever Solenoid circuit as the problem. It is a column shifter. I hope this helps! Great information, thanks for the input. Matt Roberds if you have a DC clamp meter, it is very possible the solenoid may have a few shorted turns and it exerting more current than it should. Jamie |
#11
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Brake light fuse blows intermittently
amdx wrote: My daughters 97 Avalon blows the brake light fuse about every other day. I thought I'd eliminate some wiring as a troubleshooting procedure. There is a connector block on the side next to the drivers foot. I found the brake light wire at the connector and in the trunk. I cut the wire at the connector and ran a new wire from the front to the trunk, I also cut the wire in the trunk, and wired the new wire to the brake lights. That leaves just a short old wire in the trunk going to both the left and the right brake light. The fuse opened again a couple days later. Is there anything internal to the brake lights that could short to cause the fuse to blow? There is at least one other circuit run by that fuse, there is a shift lever release (solenoid?) mechanism. You must push the brake pedal to move the shift lever. Any help? Have you replaced the bulbs? I've seen them fail with internal shorts. One was between the turn and parking light, and it would run the battery down if the radio was left on. Shorting the two circuits together would leave the accessory powered circuits live without a key. |
#12
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Brake light fuse blows intermittently
amdx wrote:
Very helpful, The first diagram let me learn that I have bypassed the "light failure fixture" with my new wire. Sites like the above tend to come and go, so it might be a good idea to grab the PDFs now and stash them. Those PDFs are from the Mitchell repair manuals; some large public libraries subscribe to them and keep them in the reference section. Sometimes the library has electronic copies that you can print, but print a test page or two before you go crazy; some of them are scanned from the paper manuals at relatively low resolution. The official Toyota wiring diagram is a slim book by itself. It doesn't have much theory of operation or troubleshooting info (those are in the thick volumes of the factory service manual) but it does give you a nice color wiring diagram. The dealership may be able to get you a new one for $30 or $40; sometimes you can snag one used for $20 or so. Mitchell adapts the wiring diagrams from the different manufacturers into their "house" format. This is probably easier to follow for an independent mechanic who works on lots of makes, but if you just have one car, sometimes it's easier to follow the factory wiring diagram. Ideally I would like to separate the two circuits as close to the fuse as possible. It looks like the split happens inside the "driver's side j/b"; that's where the switched wire from the brake light switch forks. Often these junction boxes live on the back side of a fuse panel or otherwise close to the fuses. Usually the junction box is kind of a flat plastic thing with connectors around the edge; the inside is sometimes zillions of flat stamped metal strips, arranged in layers, insulated by the plastic housing material. It might be hard to get at the circuit inside the junction box; doing it at the junction box connectors is probably easier. Matt Roberds |
#13
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Brake light fuse blows intermittently
My daughters 97 Avalon blows the brake light fuse about every other day.
I thought I'd eliminate some wiring as a troubleshooting procedure. There is a connector block on the side next to the drivers foot. I found the brake light wire at the connector and in the trunk. Modern cars have lots of things connected to the brake circuit: cruise control computer; engine management computer (strange, but true); "burned out bulb" sensor circuit; as well as the shift lock-out solenoid. You might unplug one section at a time from the harness for a week and see if it still blows. "Long term" troubleshooting... Good luck! |
#14
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Brake light fuse blows intermittently
On 5/16/2013 1:37 AM, Sparky wrote:
My daughters 97 Avalon blows the brake light fuse about every other day. I thought I'd eliminate some wiring as a troubleshooting procedure. There is a connector block on the side next to the drivers foot. I found the brake light wire at the connector and in the trunk. Modern cars have lots of things connected to the brake circuit: cruise control computer; engine management computer (strange, but true); "burned out bulb" sensor circuit; as well as the shift lock-out solenoid. You might unplug one section at a time from the harness for a week and see if it still blows. "Long term" troubleshooting... Good luck! Yes very long term, my daughter comes to town once a month or less. Last report, she said she pulled a defective fuse and some little pieces of wire came with it. After replacement it has lasted 3 days, more time than any fuse in a month. This didn't really make sense to me, but I can hope that was a cause to the problem. Mikek |
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