1986 M1008 glow plug solenoid stuck?

[ChromeChicken]

I recently bought my 1986 M1008 and it immediately started draining the batteries. I have verified that my alternators are good. The passenger side is fairly new and the driver's side was replaced with one from NAPA. Both batteries are new Group 31, though I had my back battery fail and not sure if the truck caused it or not. Either way, it has two batteries in it now.

When I connected the back battery, the cables arced to the battery post. The same thing happened when I connected the front. Near as I can tell the battery wiring is factory and correct.

I noticed my glow plug solenoid was getting extremely hot even without the ignition in the wait position. I believe this is the source of my battery drain. What caused this, and how do I fix it?

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[MarcusOReallyus]

First, disconnect the bugger and charge your batteries!

Now, to figure out why it's stuck....

First thing is to understand how it works.

I'll give you a quick shortcut:

Take note of where each wire is connected. Better yet, label them. You'll have a Big Red One, a cluster of big orange ones on the other big terminal, a small orange wire (hot when igntion is on) and a small blue one. These last two are on the small terminals.


With the relay completely disconnected, measure continuity across the two LARGE terminals. There should be NO continuity. If there is continuity, i's stuck. Replace the relay. Done.

If there is no continuity, apply 12v to the relay terminal that had the small orange wire. Now apply ground to the terminal that had the little blue wire. (You should hear/feel the relay CLUNK.)

Now measure continuity across the two LARGE terminals. There should be a good connection. If there is none, replace your relay.

Remove the blue wire terminal. Measure continuity again. Should be none. (This is just a double check.)

If all of that works, it may be that your controller card is shot and is switching your relay ON all the time. To find out:

With the relay still disconnected, measure continuity from the disconnected blue wire to a good ground. There should be NO continuity. If there is, you have a problem with your controller card. That blue wire is switched by the controller card to provide ground WHEN THE GPS SHOULD BE ON. If it's grounded all the time, the relay is on all the time, and your GPs are hot all the time, and your batteries are drained all the time.

Now, you also need to test that small orange wire that you disconnected. Use the volt meter and verify it has 12v when the key is on, and no voltage when the key is off.


All that said, if your relay was stuck on, test your glow plugs, They might be shot.

 

[ChromeChicken]

Thank you for your straightforward response and diagnosis steps. I'll give it a shot tomorrow and report back.

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[LT67]

I recently bought my 1986 M1008 and it immediately started draining the batteries. I have verified that my alternators are good. The passenger side is fairly new and the driver's side was replaced with one from NAPA. Both batteries are new Group 31, though I had my back battery fail and not sure if the truck caused it or not. Either way, it has two batteries in it now.

When I connected the back battery, the cables arced to the battery post. The same thing happened when I connected the front. Near as I can tell the battery wiring is factory and correct.

I noticed my glow plug solenoid was getting extremely hot even without the ignition in the wait position. I believe this is the source of my battery drain. What caused this, and how do I fix it?

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Is the truck still the factory 24v or has there been a full 12v conversion done to it?

 

[MarcusOReallyus]

If all of that works, it may be that your controller card is shot and is switching your relay ON all the time.

Whoops. There's another possibility. It might be that somewhere your little blue wire got shorted to ground. ( ♪♪ Somewhere over the rainbow, shorts are blue.... ♫ * )

That would keep your GPs energized even if the card is okay. To verify that, pull the card out and test the blue wire for continuity to ground. If it's shorted to ground, you need to follow it and find out where. (♫ Follow the little blue wire! Follow the little blue wire! Follow the follow the follow the follow the Follow the little blue wire! ♫ Ooohhkay. It's quite clear here that somebody needs a vacation!! )

That's not a high probability, but it should be verified before you spend big bucks on a new card.




(* Sorry, Judy.)

 

[ChromeChicken]

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[ChromeChicken]

Whoops. There's another possibility. It might be that somewhere your little blue wire got shorted to ground. ( ♪♪ Somewhere over the rainbow, shorts are blue.... ♫ * )

That would keep your GPs energized even if the card is okay. To verify that, pull the card out and test the blue wire for continuity to ground. If it's shorted to ground, you need to follow it and find out where. (♫ Follow the little blue wire! Follow the little blue wire! Follow the follow the follow the follow the Follow the little blue wire! ♫ Ooohhkay. It's quite clear here that somebody needs a vacation!! )

That's not a high probability, but it should be verified before you spend big bucks on a new card.




(* Sorry, Judy.)

Interestingly, there's a tiny bit of continuity from the blue wire to ground with the card pulled and the wire disconnected from the solenoid.

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[Barrman]

The new alternator from NAPA. Is it an isolated ground unit? The theory is the drivers side doesn't have to be, but if the passenger side isn't, that could also be a short.

 

[MarcusOReallyus]

The new alternator from NAPA. Is it an isolated ground unit?

Probably not, but you are the one who has it in hand. Test it. You could test it by installing it, but that would result in some interesting fireworks if it's not.

A meter might work better.

 

[ChromeChicken]

It's an isolated ground unit, the charging system is working fine according to the meter. There's a very slight reading of continuity at the blue wire, but I haven't checked it for resistance, not sure what the resistance should be if I did. My glow plug controller card is new. Ouch$$$

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[MarcusOReallyus]

How are you reading continuity to ground at the blue wire?

 

[ChromeChicken]

How are you reading continuity to ground at the blue wire?

I have the solenoid wires and batteries disconnected, measuring from the wire to a solid ground in the engine bay.

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[MarcusOReallyus]

With what instrument?

 

[ChromeChicken]

A multimeter, a cheap one.

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[MarcusOReallyus]

*sigh*

On what setting? What actual readings are you getting?

 

[ChromeChicken]

*hides shame* I'll retest tomorrow and take a better look.

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