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Discussion Starter #1
Howdy. So when I bought the Suburban (1987 if it matters), the PO mentioned that he sometimes had issues with the glow plug light not turning on, but so far I hadn't had any issues until today. Basically I turn the key on, all other lights come on, but no glow plug light. Tried to turn it on/off a couple times, tried to crank for a few seconds, but nothing. So I look under the hood and realize that more of the wiring had been hacked up than I originally realized. Anyone got any tips on where to start looking/tracing things? Any pics of what it's supposed to look like at the controller? I tried wiggling wires but nothing obviously wrong. All tips appreciated.
 

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Ronald Reagan fan
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Check your inhibit switch in the coolant crossover up front.Its a 2 wire switch.Ensure the terminals are clean and not loose.You can also unplug both terminals and join them together with a short wire for testing purposes.If the glow plugs come on when you’ve looped both terminals on that connector the switch is bad. Also ensure the studs on the controller are clean and tight.One stud is alive at all times while the other will have voltage with the ignition in RUN mode providing everything else is functioning okay within the circuit.

Anyway check your inhibit switch and let us know how it goes.
 

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Discussion Starter #3
Ok, just to make sure the inhibit switch is open when cold, or open when hot? Trying to measure continuity across it, want to make sure I've got it right. Thanks,
 

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Ronald Reagan fan
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Ok, just to make sure the inhibit switch is open when cold, or open when hot? Trying to measure continuity across it, want to make sure I've got it right. Thanks,
The switch should be open when coolant temperature reaches 125F.It should be closed on cold start up and have continuity at that time.
 

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Discussion Starter #5
well been busy with work and I haven't had time to dig out the circuit tester yet, but I was looking around and I found this color diagram on a CUCV site - is this basically the same as our civilian 6.2s? This looks like it would come in handy, as long as it's the same.
637230
 

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Whistle Pigs Are Cool
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Make sure that the female connectors in the GP controller harness are not bent! I had inadvertently bent two when diagnosing the wiring with my test light.
 
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Ronald Reagan fan
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You should use this diagram.This is for the 1985 civilian and later years of the 6.2
 

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Discussion Starter #8
OK well just to update, thanks for all the tips. Somehow with all my probing, testing, and wiggling, now everything works again. (the temp switch tests ok, and is working apparently)
So I guess the moral of the story is to go through all your connections and make sure they're ok, even if they look fine. Should I just unplug every single one and maybe lightly sand the ends? Just wondering what I can do to get everything in good order. with 30+ year old electricals, I'm sure this isn't the only system that is maybe a little loose.
Thanks,
 

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Discussion Starter #9
Well after the previously described wiggling worked for a few months, but now it's back to not working. I would like to pull the main plug off the controller and clean up all the connections, since it seems like wiggling that plug is what makes it work again. So I'm guessing one of those connections is loose.
However, it doesn't seem to pull off. Is there a clip or something holding it in? I don't want to yank it out and break anything. Once it's unplugged, is there a way to pull the individual wires out and clean them up too? I'd like to go through everything in that pin connector and get it solid so this doesn't happen again in a few more months. Thanks,
 

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Eagle Eyes
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If I remember right, there is a clip that secures the main harness plug to the controller body. Hard to get to over all. I think the clip is one, dead center, facing front of truck.
Remember to unhook batteries and clean the two main terminals.
Can use the dark colored NO-OX electrical grease on everything.

If the controller ends up bad, they can wear out, replace only with a ACDELCO or a CLUM Relay. Don't use anything else.

Besides the dashboard light, you should be able to hear it click on and off.
 
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