Hello everyone,
I recently modified my glow plug controller circuit to a manual push button and wanted to share my experience in hopes of helping others. To start off, my truck is a 1993 7.3 IDI with a factory turbo. This put my glow plug controller on the passenger side of the engine instead of on the back behind the air cleaner. I had installed a new controller about 5 years ago and it melted apart as most do these days. I was able to use parts from the old controller to keep from cutting apart the stock engine harness. I purchased a diesel glow plug relay from napa (part number: GPR205). This is just a simple solenoid but it is triggered by a positive and a negative (must complete the circuit to trigger). I mounted the relay to the stock plate on the side of the engine where the controller was with a couple of self tapper screws. The stock controller uses a 12v wire pair that is used to power the stock controller, all it is is 12v power when the key is on. I hooked that pair to the (I) terminal on the relay. I then ran a wire from a ground in the dash to my momentary switch, then from the switch, through the firewall to the "S" terminal on the relay. For the "wait to start" light, it needs ground to activate on the dash so I cut the plug off the stock controller, so I didn't have to modify the stock engine harness, put a ring terminal on it, and connected it to the "S" terminal on the relay as well. Now, from what I've read from others in the forum, you should not run the plugs more than 8-10 seconds to avoid melting them apart in the engine. Part of why I wanted the wait to start light to function was to see if my ground shorts and turns my plugs on while I'm driving so I can turn off the key to kill the power before they melt. Now they work great, I don't have the annoying clicking, and I don't have to run them every time thus increasing the lifespan of the plugs themselves. I would assume a similar setup would work on the 6.9s as well but I do not know. I will attach a few pictures of my completed work.

New relay with wires labeled.

Dash Switch installed under the steering column

Old fried stock controller

 

I could be wrong here but I thought the factory harness used 14 gauge fusible link wire to each plug and that the 10 gauge brown wire was also fusible link so that should offer some protection as well. I ditched the factory harness and ran a 2 gauge wire from the relay to a fused power distribution block and then ran a fused 14 gauge to each GP. I like your mod in terms of added measure of safety but it is easy to not see those lights on the dash--I've had the FuelFilter light illuminated but only noticed when the engine seemed down on power while pulling a hill, so no idea how long the light was actually on. I have wired in a large flashing red light with a built in alarm for EGTs and coolant temp and I suppose you could wire it so that if your wire shorted to ground and activated the plugs it would activate a 12v alarm.

 

I agree with you on the alarm, I probably will add that. On the fusible links to the controller, mine was a little modified before I got to it so they weren't there. It's not connected directly to the battery but to what i assume is some sort of solenoid on the fender right behind the battery. I had assumed that may have had a layer of protection in that. Do you think I should add a large fusible link to that 4ga wire feeding the glow plugs?

 

If your name is Gabe then we share the same name. I haven't dug into the GP wiring in a long time but I thought the original two yellow wires feeding the solenoid had fusible links but I could be wrong. When I redid mine because the harness and wiring was disintegrating I added a mega-fuse to the 2 gauge wire feeding my plugs but I still have the factory yellow wires feeding the solenoid. I am by no means an expert or a professional on automotive wiring or electrical in general but it seems that everything is supposed to fused somewhere, just in case. It's pretty easy to add a mega-fuse and tuck it onto the fender.