On 9/24/2019 9:04 AM, Jim Wilkins wrote:
"Terry Coombs" wrote in message
...
When I got my truck back from our son , lots of things that he just
couldn't be bothered to fix . One thing is the radio power supply .
He did tell me that the radio had "died" , turns out the fuse (in
the fuse block) keeps blowing . I've got the dashboard apart enough
to check the wiring harness and supply wires , can't find any cuts
or anything that looks like damaged insulation ... it works just
fine sittin' in the driveway , but within a few miles driving it
blows the fuse . I figured it was the radio/CD player unit so I got
a new one , does the same thing . I'm really puzzled by this , from
the way the fuse was spattered it's got to be a dead short to ground
. I think it very unlikely that the new radio/CD unit is bad - the
old one did work when I replaced the fuse , for a few miles same as
the new unit . This is an '86 GMC pickup , I'm hoping someone here
might be aware of a known problem area that I might check ... I
gotta have tunes !

--
Snag
Yes , I'm old
and crochety - and armed .
Get outta my woods !

Check/clean the battery connections.

If connector vibration momentarily disconnects the battery from the
charging circuit, the alternator output voltage will rise until a
protective clamping device somewhere, like in the radio, conducts
enough current to limit it. The voltage regulator tries to cut off the
alternator field current but can't remove the current already flowing
in the field winding.

https://en.wikipedia.org/wiki/Load_dump




Â* Wouldn't that blow the smaller fuse in the radio itself before the 15
amp supply fuse ?

--
Snag
Yes , I'm old
and crochety - and armed .
Get outta my woods !