I'm totally lost. I tested the solinoid output (to the plugs) and had 7 volts. I then removed my air cleaner and replaced all my glow plugs, put the air cleaner box back on and now I have no voltage going to my plugs??? I have 12v battery, 12v accessory on (key) , 6volts to ??? on the other small terminal, but nothing on the plow plug terminal. I did nothing else than replace the glowplugs that were all dead (no contunity due to me jumping them with 12v before I knew they were 5v) I would even just override all the automatic crap and just have a toggle switch but I can even jump the solinoid. I have replaced the solinoid with another and have the same problem.

 

You may have burned out the fusible links they should be blue.......

What year is the truck............

 

1994, where would these links be???

 

Visit this gallery for the GP system schematic........

http:///showphoto.php?photo=21674&pa...t=1&thecat=500

Please go to Quick links at the top and put all the info re your truck, makes life and assistance much easier.....thanks.

 

When they say fuse links, do they mean thoes are regular fuses or additional in line fuses? Any idea the location of thoes fuses that diagram shows, there are 6 or so.Thanks for that link.

 

This is the glow plug relay.
Do you not have voltage on the yellow battery terminal?
This is a direct connection to the positive battery terminal and is always hot reguardless of the key position. The fuseable links should be on the passenger side inner fender. They probably look just like wire of a different color has been spliced in the circuit that is about 6 inches long. Some of them have a molded rectangular block of plastic on them. Also check the plug in the wiring harness near the dip stick where the engine harness plugs into the body harness, the two large wires in that plug are power to the relay. If I remember right they are yellow. The connector may have corrosion on the inside of it.
When the key is on you should also have battery voltage on the red ignition terminal.

 

I have power from the battery, I have +12v from the ignition, I have 6v output on the white wire, I have no volts on the glow plug side of the solinoid. I'll check for thoes fuses, THANK YOU.

 

I have the exact same problem - can't get the relay to close. I have power at the battery terminal but can't get power the other side, I sthere a fuse on that side as well?

 

OK here you go.
The white wire out of the controller goes to ground when the glow plugs are to come on.
Either the black ground wire is not making connection to the block or the controller is dead. The black wire is usually under one of the bolts that mounts the relay to the block, remove the bolt and clean the wire and block with a wire brush. Then reinstall everything as it was. Since the yellow wire is always hot you should remove the battery cables before you unbolt the relay so it does not short out if the relay touches anything while unbolted.
If you have power at the red and yellow terminals on my picture when the key is on, the fuseable links are good, so you can skip that test.

Also as an afterthought, look where the small yellow and small green wires are connected. There is a contact in the bi-metal strip that opens under overload conditions.
This contact may have been bent or had something get stuck in it that is holding it open. Check for voltage on the terminal while the key is turned on by someone else.

You may also ground the white terminal to the engine block for a few seconds to see if the relay closes, but keep grounded for under 10 seconds or the glow plugs are going to toast.

A wire run inside the cab that grounds the white terminal through a momentary switch that you can hold down for a few seconds will convert the glow plugs to manual control if the relay is good.

 

Thank you so much Dave, I didn't think about grounding a wire to manually trigger the solinoid. I'll get to looking at the grounds and let you know. thank you x10

 

I can now jump the sloinoid but I get +12v to the glowplugs. The plugs say 5v and I thought before all this started I had 6v out of the solinoid. What is the correct voltage the solinoid should allow to the plugs?

 

?? Anyone?

 

The solenoid puts battery voltage to the glow plug wires if you have no glow plugs hooked up to the circuit.

So if you unplugged all the glow plugs and energized the relay you should see exactly the same voltage at the plugs as what you have in the batteries.

Due to the large amp draw from the glow plugs heating, the voltage drop to the glow plugs through the rather small wire running to the plugs, will be around 7 or 8 volts when checked at the glow plug connector with all the glow plugs hooked up and working

Check all connections for corrosion from the battery to the glow plugs, there are several. After you clean them an application of oxide inhibitor will keep things working much better. You can get an oxide inhibitor at an electrical supply house or good auto parts supplier.

The 6 volt glow plugs installed in a 12 volt circuit is why they heat so fast.
It is also why you should never have them on for more than 10 seconds at a time.
The tip of the glow plug will be white hot in a matter of seconds.