On 29.05.16 19:27, Snuffy "Hub Cap" McKinney wrote:
This is an intermittent problem that only happens when driving with the headlights on -- but does happen every time. Any ideas how to troubleshoot it?

For awhile the needle would oscillation between the normal 50-60% position a few degrees after driving a half hour or more with the headlights on. Then I cleaned all the connections in the starting systems from battery terminal to hot connections and grounds, and the problem stopped.

Then last week, I had driven to a store at dusk with the lights on - no problem indicated. I left the lights on for 20 minutes while in the store. Then when I started, the battery needle start oscillating from 50% to 100% regularly, and the battery warning light started blinking off and on.

Car was running fine so I turned off the headlights and just put on the parking lights so I could drive the 2 miles home. After driving about 1/2 mile the oscillating and flashing stopped.

I have tried to duplicate the problem so I could show a mechanic, but all is back to normal for now.

Without knowing anything, I would guest that the computer detected some kind of low voltage and the swinging and flashing was an attention-getter, and not the actual reading.

Any ideas how to troubleshoot this?




Leaving the lights on 20 minutes would put more load on the alternator
when you did start the car. The first thing that comes to mind is that
for some reason the alternator is unable to work properly under high load.

The second thing that comes to mind is some serious sounding problems
have simple solutions. Higher load makes the alternator work harder.
It can be something as simple as a slipping belt. I'd tighten or
replace it before rebuilding the alternator. Yes, I've seen it happen
more than once. .
---

Thanks for all the help. Still trying to find the time to spend TS...

Last night I was able to catch it cycling just now. No time to check at the alternator tonight, but here's some voltages at the battery terminal.... Turn signals seems to cause the cycling tonight, although I have seen it cycling with just the lights on.

Battery with engine off - 13.6
Turned engine on
Idling with no lights - 15.0 steady
Turned on parking lights - 15.0 steady
Turned on headlights - 15.0 steady
Turned on headlights and turn signal - 15.2-15.8 cycling
No lights, turn signal on - 15.2-15.8 cycling

That sounds like a defective regulator or generator
going on/off.
Which would suggest the two voltages.
Bad wiring would produce a different pattern.