Did I just fry my glowplug card

[Russm]

Seems my resistor failed. 25.98 volts at the glow plug relay. Probably toasted a few plugs too.

Sad panda if the card is toast, it's a new one just over a year old.

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[NDT]

Resistors fail open. You will see that voltage if numerous glow plugs are open.

 

[Russm]

I think I understand now after finding some other posts: 24v is normal unless the glow plugs are glowing.

Next question: Purple wire in the diagram - is it supposed to be 12v or 24v with the key on?

Lastly: is there a method of troubleshooting the glow plug card? Mine is the new one from Mr. Hillbilly.

Backstory: stock glowplug function existed before the transmission issues. truck has been sitting for a few months while I worked out transmission issues. These are fixed but glow plugs suddenly do not activate. Jumping the relay resistor->glowplugs activates glowplugs. Jumping the other 2 pins with an external 12v activates the relay and the plugs. Currently the wait light flickers on then off for a fraction a second when turning key on. Relay does not engage. Currently going through and replacing crimp style connectors with solder+heat shrink in the hackjob that was present before I reestablished stock function earlier this year.

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[WWRD99]

I think I understand now after finding some other posts: 24v is normal unless the glow plugs are glowing.

Next question: Purple wire in the diagram - is it supposed to be 12v or 24v with the key on?

Lastly: is there a method of troubleshooting the glow plug card? Mine is the new one from Mr. Hillbilly.

Backstory: stock glowplug function existed before the transmission issues. truck has been sitting for a few months while I worked out transmission issues. These are fixed but glow plugs suddenly do not activate. Jumping the relay resistor->glowplugs activates glowplugs. Jumping the other 2 pins with an external 12v activates the relay and the plugs. Currently the wait light flickers on then off for a fraction a second when turning key on. Relay does not engage. Currently going through and replacing crimp style connectors with solder+heat shrink in the hackjob that was present before I reestablished stock function earlier this year.

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I'd go after the temp sensor on the rear of the drivers side head. That's supposed to trigger the ground on the board to turn on the glows. Does it start after you jump the glow plug relay? I can only assume it's cold up there now and mine need glows at 50 degrees. Check the ground at the back of the passenger side head to the cab too...or check to see there is one to the cab.

 

[Russm]

I'd go after the temp sensor on the rear of the drivers side head. That's supposed to trigger the ground on the board to turn on the glows. Does it start after you jump the glow plug relay? I can only assume it's cold up there now and mine need glows at 50 degrees. Check the ground at the back of the passenger side head to the cab too...or check to see there is one to the cab.

Started instantly at 0*F the other day after jumping the relay. Will check those grounds and the resistances off the temp sender. Tracking it's supposed to be about 300 ohms at 125* and ~30,000 ohms below freezing.

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[WWRD99]

Started instantly at 0*F the other day after jumping the relay. Will check those grounds and the resistances off the temp sender. Tracking it's supposed to be about 300 ohms at 125* and ~30,000 ohms below freezing.

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I backprobe the wires when it's cold and see what it is plugged in, then warm it up and see if it changes. The ohm thing is good but you really don't know if it's working...probably do that with the key on and off and see if there is a change as well. I think it would be very easy to do that at the glow plug card since it's right there hanging under the dash. You can go off the pic you posted to find which wires they are...easier than going under the hood. Could be a crusty connection at the card too can pop it out and in and see if it works...can do the same thing at the sensor.

 

[Russm]

Well I did it. Not the right way but it's fixed:

Found a few more random chopped wires sticking out of the fuse box. This truck used to be a police vehicle maintained by an idiot so you can imagine the hackjob under the dash.

Probed some more with the multimeter, found the 12v source wire (pink) was reading basically zero with key on. Also found the ground wire was no longer grounded. All fuses looked good. As far as I could tell both pink and ground wires were intact until they disappeared behind the fuse box.

This was a pickle.

Spliced a new 12v from an ignition slot on the fuse box and also spliced a new ground going to the Xmas tree spider ground thingy under the dash on the wall.

Normal function is restored.

Short of transplanting a known good wire harness from a different truck I don't think I'll ever be able to restore it to fully stock wiring. There's too much hacked up.

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