Glow Plug Relay Mod

Ok here’s a shot of the gpr stuff I did. Yes I know its horrible under there and needs cleaning but I don’t have a garage and the weathers crap here.


All I did was remove the wire to the pcm. The pcm provides ground on that wire to energize the gpr. The clean looking red lug with the blue wire is the one I added after removing the pcm’s wire. The other small wire on the opposite side terminal is key switched positive.

Then I used a bolt with 2 washers and a nut and put a lug connector on the wire I added and joined the pcm’s lug and the one I added together with the bolt and washer deal. Then taped it up to be on the safe side. The other wire I added has a lug on it and is bolted where the pcm wire used to be.

Then the 2 wires I added are connected to a switch inside. When the switch is off the gpr cannot engage no matter what. When the switch is in the on position the gpr functions like it did from the factory.

I will be adding a 3rd wire to the glow plug lead on the gpr to connect to the led spot on the switch so the switch will light up when the glow plugs have power.

Also after doing some research on how the system works we all were partial right. I said it runs no matter what the temp and others said it was controlled by oil temp and the baro sensor.

It runs no matter what up to 2 full minutes depending on what the pcm reads from the oil temp sensor. But it ALWAYS comes on even if the oil is red hot. It just doesn’t stay on long if the motor is fully warmed up.

The oil temp and the baro sensor determine how long the gpr runs which can be as little as a few seconds if the motor is completely warm and it directly effects how long the wts light stays on.

The computer runs the light to let you know when to start the truck, not when the glow plugs cut off. Then it keeps the glow plugs on longer than the light to cut down on emissions.


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