I ordered a new GP relay, no click, 0 volts at bottom post of relay. two middle posts have about 12v and the top post is 24v. Truck is new to me, the relay on there has a 12v sticker on it. if I understand correctly, when the relay energizes, the voltage at the top post should go to the bottom post and energize the GP's. I just put in new 13G's, and don't want to burn up the new relay or GP's. all of the schematics don't show what the voltage is supposed to be at the top, and I though the resistors were supposed to drop the voltage to 12v. am I missing something? this is a driver truck, not a restoration, so I have considered doing the doghead resistor bypass, but can't seem to find the right link. any help is appreciated thanks
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GP relay voltage readings
- Thread starter hrt119
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Your voltage readings are correct. The relay coil voltage is 12 v, this controls the relay. The Pink/Black wire has +12 volts on it. When you ground the Light Blue wire, the relay will close. These are the two smaller terminals.
The closing of the relay is connecting the 24 volts from the large top post to the large bottom post. This provides voltage to the glow plugs. Once the relay closes, the voltage will drop to 12v. This will only drop to 12 volts once you complete the circuit with all 8 GP connected to the voltage source.
There is a good list of information on your vehicle available here:
CUCV Helpful Threads
The resistor bypass information can be found here:
CUCV Resistor Bypass
The closing of the relay is connecting the 24 volts from the large top post to the large bottom post. This provides voltage to the glow plugs. Once the relay closes, the voltage will drop to 12v. This will only drop to 12 volts once you complete the circuit with all 8 GP connected to the voltage source.
There is a good list of information on your vehicle available here:
CUCV Helpful Threads
The resistor bypass information can be found here:
CUCV Resistor Bypass
thank you,,, appreciate the help,, still trying to figure out this truck and these forums,,, so much information
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- State College, PA
No problem.
Let us know if you need any more help or assistance with things.
Let us know if you need any more help or assistance with things.
MarcusOReallyus
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The "no click" and 12v on both small terminals may indicate that the relay is not being grounded (blue wire) by the controller (under the dash).
You can test this by turning on the key (should see 12 at the small terminals) and then manually grounding the small terminal with the blue wire. Use a jumper.
If this gets you a click, and 12v at the lower big terminal, you have a problem with the controller card circuit. That could be the card itself, one of the sensors it "listens to", the blue wire itself, or the ground to the controller card.
That grounding is up under the dash by the parking brake, and it does get rusty. Look for a black wire going to a 6 pronged connector. Clean that up whether you think it needs it or not. Make it shiny bare metal, apply a bit of dielectric grease, and it won't bother you for a while.
That's not an exhaustive troubleshooting guide, but it should give you a few quick things to look at. The links antennaclimber posted above are well worth your time.
(BTW, if you try grounding the blue wire, get a click, and a bunch more than 12v at the lower big terminal, you have the grounding problem already mentioned, and one or more of your GPs are history.)
You can test this by turning on the key (should see 12 at the small terminals) and then manually grounding the small terminal with the blue wire. Use a jumper.
If this gets you a click, and 12v at the lower big terminal, you have a problem with the controller card circuit. That could be the card itself, one of the sensors it "listens to", the blue wire itself, or the ground to the controller card.
That grounding is up under the dash by the parking brake, and it does get rusty. Look for a black wire going to a 6 pronged connector. Clean that up whether you think it needs it or not. Make it shiny bare metal, apply a bit of dielectric grease, and it won't bother you for a while.
That's not an exhaustive troubleshooting guide, but it should give you a few quick things to look at. The links antennaclimber posted above are well worth your time.
(BTW, if you try grounding the blue wire, get a click, and a bunch more than 12v at the lower big terminal, you have the grounding problem already mentioned, and one or more of your GPs are history.)
thank you,,, i'll give that a shot, appreciate the help