1972 GMC Sierra c2500, electric

[Captain J]

Hi, 2 issues
One, when I drive for an hour or so, and I turn off the truck, it won’t start, starter is slowly turning like with a low voltage battery, but when I leave the truck to cool, it will start again. Any thoughts.
2ed, this wire runs on the front grill, from the left side to near the battery on right side, it’s disconnected near the battery has 2 small glass fuses.
What’s for?
Where it should be connected to?
Pictures attached,
Thanks

[demian5]

That is for you your ammeter only. I do not believe it would have any effect on your starting.

Check all of your grounds on the motor, body, frame, make sure they are all clean and tight as well as your battery cables.

[Doug's68SS]

my 68 started doing that, it has a 396 in it and the passenger exhaust manifold had a crack in the bottom that was heating up the starter. would start when it cooled off. I installed a heat shield until I got a manifold to replace it and then I left the heat shield in place.

[Captain J]

Demian5, thanks for your reply
Is it hooked to the battrey? Because when I tried it shorted out, blew a mini glass fuse.

I cleaned all my grounds, battrey cables, starter connections. I may put new battery, even though the battery is an Optima.

[Captain J]

Doug’s68ss, thanks for the tip. mine has the heat shield, but I’ll recheck it,

[demian5]

Originally Posted by Captain J

Demian5, thanks for your reply
Is it hooked to the battrey? Because when I tried it shorted out, blew a mini glass fuse.

I cleaned all my grounds, battrey cables, starter connections. I may put new battery, even though the battery is an Optima.

You will need a DVOM to check for a short to ground somewhere in the circuit that is blowing your fuses (hence the reason it is already disconnected).

https://www.google.com/search?ei=WIs....0.52WKpa_kMwU

I believe it connects to the plastic junction block that attaches to the pass fender.

[allchevy58]

Battery may have a shorted cell, try jumping it when it does it again and if it starts, buy a new battery. Not sure about second issue, have to look at my truck. Believe that wire bolts to the fender on the battery side, grounded.

[Captain J]

Allchevy58, I’ll buy new battery, and see.
Ok, thanks

[demian5]

Originally Posted by Captain J

Allchevy58, I’ll buy new battery, and see.
Ok, thanks

You can have it tested for free. I had a red top optima last 10 years in my 64 impala.

[Captain J]

Originally Posted by demian5

You will need a DVOM to check for a short to ground somewhere in the circuit that is blowing your fuses (hence the reason it is already disconnected).

https://www.google.com/search?ei=WIs....0.52WKpa_kMwU

I believe it connects to the plastic junction block that attaches to the pass fender.

You mean (the plastic junction block) the negative (ground) side? Or positive side?
Because I am confuse, if it needs a ground, why not ground it to the driver fender? Because when I tried to hook it to the positive junction, it shorted out blowing one of the tiny glass fuse.

[Captain J]

Originally Posted by demian5

You can have it tested for free. I had a red top optima last 10 years in my 64 impala.

We have no dealer for Optima, where I live, however I put a new battery and it cranked right away, which means the Optima battery is bad. But I still need to test the starter after a long drive, if the issue comes back.

I’ve 2 other Optima in my other trucks and they work great.

[demian5]

Originally Posted by Captain J

We have no dealer for Optima, where I live

A battery load test is a battery load test, don't need a specific dealer for that.

[Captain J]

Originally Posted by demian5

A battery load test is a battery load test, don't need a specific dealer for that.

Oh, ok. I misunderstood, sorry

[allchevy58]

Your wire should run to a positive block on right fender. You must have a short. Wire diagram shows it going to high beam switch and headlight switch. Looks like it tees off to alternator too. Someone spliced in the red wire to the black with the flat fuse.

[rockyrivermark]

I had the same problem. It was heat soak in starter coming off the exhaust.
Put a heat shield on and problem solved.
Mark

[Captain J]

Originally Posted by allchevy58

Your wire should run to a positive block on right fender. You must have a short. Wire diagram shows it going to high beam switch and headlight switch. Looks like it tees off to alternator too. Someone spliced in the red wire to the black with the flat fuse.

Thanks for the pictures, the headlight switch works ok, so is the the high beam, but I’ll recheck.

[Captain J]

Originally Posted by rockyrivermark

I had the same problem. It was heat soak in starter coming off the exhaust.
Put a heat shield on and problem solved.
Mark

Thanks

[Captain J]

Originally Posted by Doug's68SS

my 68 started doing that, it has a 396 in it and the passenger exhaust manifold had a crack in the bottom that was heating up the starter. would start when it cooled off. I installed a heat shield until I got a manifold to replace it and then I left the heat shield in place.

I did find the heat shield in my truck, can you pls send me a picture of yours or part number, and from where you bought yours? I truly appreciate it.

[Eddie H.]

This was a common problem with GM trucks in the 70's and 80's. It was caused by excessive exhaust heat. When I was working at a Chevy dealer , GM had a service bulletin that had us install a heat shield, along with a different solenoid and spring.

[Captain J]

Originally Posted by Eddie H.

This was a common problem with GM trucks in the 70's and 80's. It was caused by excessive exhaust heat. When I was working at a Chevy dealer , GM had a service bulletin that had us install a heat shield, along with a different solenoid and spring.

Do you know the heat shield part number, and where can I buy it from?
maybe a picture of the shield? Thanks

[Eddie H.]

Originally Posted by Captain J

Do you know the heat shield part number, and where can I buy it from?
maybe a picture of the shield? Thanks

I don't know the GM part number, but they are available from Jegs, Summit, Ebay, etc

https://www.ebay.com/itm/Satin-Alumi...RXsjrK&vxp=mtr

[Captain J]

Originally Posted by Eddie H.

I don't know the GM part number, but they are available from Jegs, Summit, Ebay, etc

https://www.ebay.com/itm/Satin-Alumi...RXsjrK&vxp=mtr

Thanks a lot

[RichardJ]

The 4 Amp fuse should be connected to the Junction block at the battery. The wire goes through the firewall connector, directly to the Ammeter. A second wire from the Ammeter comes back out to the other 4 Amp fuse.

You could have a short anywhere on those wires or something shorting the back of the Ammeter.

[VetteVet]

Common sense tells me that a bad battery would start a vehicle good when it was cold, and then not start it when it was warmed up good , rather just the opposite. Heat soak is a common problem with headers or a manifold too close to the starter.

If the solenoid will not click then it is heat soaked, and if it clicks but the starter will not turn, then the starter windings are heat soaked. When electrical items get too hot then the wires will build up too much resistance for the voltage to overcome, and no current flows to operate the items.

If the solenoid is the culprit then here is a very good work around.
Get yourself a Ford solenoid and run the purple GM solenoid wire to it and run the battery positive cable as shown with a jumper from the large terminal on the GM solenoid to the S terminal where the purple wire was originally. The result is you get a full 12 volts to the GM solenoid and it will solve the heat soak issue in most cases. If the starter windings are heat soaked then a heat shield is the best cure less buying a brand new heavy duty starter.



Another benefit of the Ford solenoid is that it takes much less current to activate it, which is easier on the ignition switch for longer life.

[demian5]

Originally Posted by VetteVet

Get yourself a Ford solenoid....

Only place where ford had a better idea...