6.2l diesel electrical problem!!!

[Jonathan_GMC]

I have a 1986 GMC 6.2l diesel and my headlights are super dim. My low coolant light keeps coming on and glow plug light turns on sporadically. It will also return to normal voltages for a short period of time before it starts acting up again. I put a new alternator in and the truck and brand new batteries. I think something is creating a draw that the alternator can't keep up with. When this is happening the volt gauge is reading a bit more than 8 volts. I think it can be a glow plug controller taking the charge but not sure.

 

[Blue Ox]

Clean and tighten all battery terminals and grounds. Particularly look at the pill between the positive cable connection on the pass side battery.

 

[Jonathan_GMC]

Okay, I'll definitely try that.

 

[mshawn]

Glow plug controller.

 

[Jonathan_GMC]

Just bought one to replace it tonight. Hopefully it will fix the problem. Thanks for the help guys!

 

[Jonathan_GMC]

I replaced the controller and it still hasn't fixed the issue. Connections are good. I don't know what else it can be if anyone else has information please let me know. Again thank for the help.

 

[Blue Ox]

It still sounds like a bad ground issue. How about the ground strap between the cab and the engine?

 

[Jonathan_GMC]

I'm going to look into that when I have some time.

 

[mshawn]

Did you replace the glow plug controller or the glow plug solenoid? I ask this because a lot of people get them confused.

 

[Blue Ox]

Did you replace the glow plug controller or the glow plug solenoid? I ask this because a lot of people get them confused.

'85 and up they were a combined unit.

 

[mshawn]

'85 and up they were a combined unit.

My 87 is separated. But that could have changed. I thought the combination started in 88

 

[Blue Ox]

I'm referring to the '85 5 pin relay/sensor module on the back of the driver side head. '84 and before had the cylindrical sensor and Ford starter solenoid looking relay mounted on the fender.

I'd post a pic, but don't have anything in my pocket right now.

 

[Jonathan_GMC]

You are definitely right, its a ground issue. Just dont know where its at. I've checked alternator grounds and the ground straps. I printed the headlight and instrument panel wiring schematics. I'm going to check all the grounds in those areas and hopefully that fixes the issue. I'm pretty sure the controller and actuator are one unit on my 86. It's a four prong connection on the intake manifold behind cylinder number 7. I'm pretty sure its a ground issue some where in the headlight harness or instrument panel.

 

[Jonathan_GMC]

After a few weeks I got it fixed. It was a poor ground connection from the core support grounds near the passenger side battery. All is well now and the truck works like a charm. Thanks for the input everyone! Hope all of you are having an amazing day!

 

[mshawn]

Great to hear you got it figured out!!!