Glow plug relay/controller questions. Need help!

I've got an 8.7, 6.9 truck (has the 88+ GP system) and the fusible link from the starter relay to the GP relay burned. So I have a few questions to get it fixed.....this truck has been reworked a time or two I think. Fusible link had already been replaced with two green 14ga? Link wires.

1. If I unhooked the Fusible link wires from the starter relay, why does my wait to start light/buzzer stay on for the normal amount of time???
2. What do I need to replace the fusible link with? What size F-link/inline fuse/circuit breaker should I replace it with specifically?
3. How do I check my GP relay/controller? An if either is bad do I have to replace them to use a push button OR can it be wired to bypass the relay/controller?

I don't care to turn a wrench on anything...I already swapped the motor and have learned tons about these trucks BUT I absolutely hate electrical work. I don't really understand wiring diagrams either but I do like hand drawn pictures haha. Thanks!

The fusible link wires have nothing to do with the controller, they just supply 12VDC to the controller relay to power the glow plugs when the controller energizes the relay.

Replace the burn't wires with 12ga, but don't run them thru the disconnect connector over the valve cover. Just run them straight from the fender relay to the controller relay.

Those wires may have burn't up because the controller relay stuck closed, sometimes the contact inside the controller relay will weld itself closed. If you have a volt meter connect the positive lead to the relay side with the Z-strip on it. you shouldn't get any voltage reading on the meter when you turn the key on, if you do then the contact is welded closed, or you can use a test lite in place of the meter.

I don't draw pictures, if you can't understand what I wrote, take it to someone that can.

Are you sure those wires going from the starter relay to the controller are 12 gauge? I thought they were 10 gauge.

If you want to replace the fusible links with something else, you will have to use a 200amp or so maxi fuse to hold the current of the glowplugs. I just bought a 99 Tahoe with a blown engine, and looking around in it I noticed it runs a large wire to the starter, and another decent sized wire to the 175amp maxi fuse that runs the whole electrical system. One of those in each wire going to the glowplugs would work. Or just replace the fusible links again.

Check the wiring over really good to make sure it's not touching anywhere and shorting out. I have already had to bypass the wiring plug that was mentioned above, it melted the connector like they all seem to do.

Here's a picture of the controller. If you want to go to manual control, just take the white wire off and tape it, then put a new wire where the white wire was, run it into the cab, and hook it to one side of a momentary pushbutton. Hook a short piece of wire to the other terminal of the switch and bolt it to a good ground under the dash. That's all you need to do for manual control.

Well I just thought that if none of the glow plugs were functioning (no power) the WTS light and buzzer wouldn't stay on the full time. That what everyone says is a tale take sign of burnt glow plugs so I'm confused still? Lol.

All the other info helps a lot though. I'll check it with a meter and run a push button most likely. And of course replace the fusible link. Thanks

These don't have a glowplug buzzer.
That's for the seat belts. Lol

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Ok, I have a question now. I have seen this somewhere before, but after a search with no results I will ask again.

I have been having problems with my GP relay as well. Today, I did the manual operation mod. Works good and reliable so far, but here is the problem, I can see the wait to start light faintly glowing. I am positive the relay isn't triggered, because the voltage is not being pulled down. Any ideas why the light would be doing this?

There are two circuits feeding the glowplug controller. You have the two main power wires coming from the starter relay. All that does is supply power to glow the plugs, nothing else.

The other circuit is the red/green wire labelled "ignition switch" in the above picture. This circuit powers the brain of the controller, and is also the source of power for the coil of the relay. When you have power on this "ignition wire"(turn the key to run) and then ground the white wire with the manual switch, then current passes through the glowplug relay, it clicks, and connects the two yellow wires to the glowplug wiring.

Well I just thought that if none of the glow plugs were functioning (no power) the WTS light and buzzer wouldn't stay on the full time. That what everyone says is a tale take sign of burnt glow plugs so I'm confused still? Lol.

Click to expand...

I have been having problems with my GP relay as well. Today, I did the manual operation mod. Works good and reliable so far, but here is the problem, I can see the wait to start light faintly glowing. I am positive the relay isn't triggered, because the voltage is not being pulled down. Any ideas why the light would be doing this?

Click to expand...

The wait to start light is controlled be the brain of the controller. The brain also controls the grounding of the white wire. If the controller brain is malfunctioning, you can do the manual button conversion and have control over the relay in the controller. The brain will still be getting power, so the wait to start light might flash or light dimly, but it won't matter, you will have control over the glowplugs since you took the white wire off.

...and I highly recommend a relay upgrade if you suspect yours is faulty. See the part number in my signature!

Ok so now a couple more questions:

1. I replace the GPC fusible link wires with 10 or 12ga? And I run two wires or only one?
(I'm thinking mine had dual 14ga, but they weren't factory)

2. If the controller itself is bad and I run a push button GP system, do I still have to replace the controller? Can I completely remove the controller???

3.

For pushbutton, all you need is a good heavy duty relay/solenoid.

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Need help with cold idle solenoid no power through wiring hot wired by switch for now

Thefarmboy21 said:

Ok so now a couple more questions:

1. I replace the GPC fusible link wires with 10 or 12ga? And I run two wires or only one?
(I'm thinking mine had dual 14ga, but they weren't factory)

2. If the controller itself is bad and I run a push button GP system, do I still have to replace the controller? Can I completely remove the controller???

3.

Click to expand...

Granted I have the old style GP setup but the concept is the same.

1. 12ga. would be just fine. If you delete the fusable link make sure to install an inline fuse holder.

2. The GP controller doesn't need to be replaced if you install a switch. The controller is basically an expensive timer. When you install the switch you bypass the controller and become the timer. Someone correct me if I'm wrong but the newer style controller has the GP solenoid built in to it. It would make sense to leave it there because the solenoid. If not you might have to switch to the old style passenger side fender mounted GP solenoid when you remove the controller/solenoid from the back of the block.

For what it's worth I had my GP controller fail ON on me last week. I simply unhooked the lead from the controller to the GP solenoid (again older style setup) and installed a switch per the write-up on this site. Problem solved.

Hope that helps.

Thefarmboy21 said:

Ok so now a couple more questions:

1. I replace the GPC fusible link wires with 10 or 12ga? And I run two wires or only one?
(I'm thinking mine had dual 14ga, but they weren't factory)

2. If the controller itself is bad and I run a push button GP system, do I still have to replace the controller? Can I completely remove the controller???

3.

Click to expand...

Don't get the wiring and the fusible links confused. The two yellow wires are 10 gauge wires feeding the glowplug controller. The fusible links protecting these 10 gauge wires are 14 gauge fusible links. They are just short undersized pieces of wire with special insulation that won't catch fire when they get hot and melt. I am going by memory, but I believe the factory diagram shows one 14 gauge fusible link in each wire.

If you want to run some other type of relay, you can get rid of the controller, but you will need to do a little re-wiring. The controller contains the large relay that is doing all the work, sending all the current to the glowplugs. And they have a nice spot where it's mounted on the controller housing, so you might as well just leave the controller since it's a good spot for the relay.

I just need to know the correct size and/or amperage fuse to run to POWER the Glow Plug relay. Normally the fusible links that run from the starter relay to the GPC.

Thefarmboy21 said:

I just need to know the correct size and/or amperage fuse to run to POWER the Glow Plug relay. Normally the fusible links that run from the starter relay to the GPC.

Click to expand...

One 200 amp fuse feeding both wires should hold it.