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wires are metal ...

   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 !
Reply to
Terry Coombs
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On Sep 24, 2019, Terry Coombs wrote (in article <qmd3tl$7ql$ snipped-for-privacy@dont-email.me):

It´s classic for sure. The power wire is bouncing around as you drive, and over time the wire insulation was worn through, allowing contact between copper wire and some part of the steel body.When you find the spot, it will be pretty obvious visually.

Solution is to find out where this is happening, and mechanically prevent further contact.

Joe Gwinn

Reply to
Joseph Gwinn

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.

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Reply to
Jim Wilkins

Just some random ideas... Does it have a power antenna? (doubtful)

Check the fuse schematic and see if anything else uses the same fuse?

Any kind of work/replacement done than might have pinched a wire underneath or shot a new screw threw a wire?

Some speaker systems run "hot leads" and do not behave well if a lead gets grounded...

Reply to
Leon Fisk

Just some random ideas... Does it have a power antenna? (doubtful)

Check the fuse schematic and see if anything else uses the same fuse?

Any kind of work/replacement done than might have pinched a wire underneath or shot a new screw threw a wire?

Some speaker systems run "hot leads" and do not behave well if a lead gets grounded...

Reply to
Jim Wilkins

  I kinda figure you're right , there's a place where it's worn thru . The problem is finding that spot ... if it was obvious I'd have found it by now . I've looked and felt as much of that harness as is available to check , nothing so far . I'm starting to wonder if it's in/near the fuse block , maybe where the under-dash wiring comes from behind the block . But it's raining today , and I'll be too busy to look into it further until Friday or Saturday .
Reply to
Terry Coombs

  Wouldn't that blow the smaller fuse in the radio itself before the 15 amp supply fuse ?
Reply to
Terry Coombs

  Nope , no power antenna .
  As far as I can tell it's only the radio , nothing else goes dead .
   Nope , no other work besides a transmission replacement . I don't think the power lead for the radio goes anywhere there .
  No powered speakers , basic stock 4 speaker system , I have some bigger speakers in a box behind the seat . I've never had any problems with the stereo system in the 12 years I've had this truck - until I loaned it to my son "for a few weeks" that turned into a year and a half . In fact , the only problems I've had were normal wear-n-tear stuff that happens with over 120k on the odometer .
Reply to
Terry Coombs

Hard to say without looking. Some fuses blow immediately, others have a time delay to allow high-current startup surges like charging the power supply capacitors. For example I can pull 70A for about 10 seconds through the 30A output circuit breaker on my home brew 24V battery charger.

Cleaning the battery connections is a good idea whether or not it helps here.

Reply to
Jim Wilkins

  And at a thousand volts ... someone else on another ng posted a link to wiring diagrams , which led my eventually to a forum post that indicates that power lead goes straight and only to the radio . It comes out of the harness with the correct other wires . I have traced that harness from the fuse block to the radio and find no damage or rubs or torn wrap . My next step will be to pull the fuse block from the firewall and check for problems on the back side . Gotta pull the plug off from the rngine side first , and that ain't happenin' in the rain .
Reply to
Terry Coombs
<snip>

Well Snag says it has four speakers. Maybe two in front and two in back...

I would disconnect say the rear pair at the radio plug and see if it still happens. If not try vice-versa...

When I was still working on radios years ago some speakers were tied directly to DC voltage/amp circuit. No output transformer and no inline capacitor. They had to be isolated from each other and ground or trouble would ensue...

Reply to
Leon Fisk

The Yellow wire is the main power to the radio, fed by a 15 amp fuse. Black is ground.

Disconnect the radio and go for a drive, see if the fuse fails. I think it will as I suspect you have a short inside the harness. The easiest fix would be to run a bypass wire from the fuse box to the radio. If it was a constant short it would be easy to find, intermittent ones can be a bear.

If you wish you can visit 2carpros.com and get the wiring diagrams, but the system isn't complicated.

Reply to
Steve W.

My electronic experience is almost all industrial and military, very little consumer. Was that an H bridge?

Reply to
Jim Wilkins

Can you extend the fuse holder and install a fuse with an LED indicator that could show you what driving conditions cause the fault?

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Reply to
Jim Wilkins

If you know where it comes out of the fuse block. cut it at about 8", connect a new wire, run that up to the radio and do the same at the other end. Give yourself 8" out of the radio connector and connect your new wire. Also, I would have taken the connector loose from the radio and drove it before I got a new radio, just to verify, harness or radio. Mikek

Reply to
amdx

  I'm thinking that Steve is right , it's inside the harness . I spent over an hour today minutely inspecting that harness for any kind of damage that might be the short . I'm tied up tomorrow and Thursday , but on Friday I'll be pulling that fuse block and probably running a new power supply wire outside the harness . As far as what conditions cause the short , that's what is weird . I have over a mile of rough (ROUGH!) unpaved road to get to the highway , the radio died a couple of miles after I hit the paved road .
Reply to
Terry Coombs

  I wanted a new radio anyway ... that one was a freebie , the back-light on the faceplate died some time ago and it has no aux inputs . As I mentioned here somewhere , I'll be looking into doing what you suggest on Friday . Tied up until then .
Reply to
Terry Coombs

You might research how to make a reliable splice in vehicle wiring, since vibrating copper wire tends to work-harden and break. When engine electronics expanded in the 1970's even the engineers had trouble with connections.

When I was wiring prototype electric vehicles the company had the proper expensive crimping tools. Soldering is usually bad because it can create a stress concentration where the wires exit the solder, which hastens breakage. The motor in my Maytag washing machine failed that way.

I don't have a 100% perfect record of crimp-splicing wires at home with cheap consumer or worn industrial tooling and like welding it's a muscle-memory type job I'm better at doing than describing.

Reply to
Jim Wilkins

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