Bypassing the Glow Plug Controller 6.9l IHC

[mankypro]

Ok, so presumably the stealership is going to replace my GPC with a new one here in the next day or so. I however, want to by pass it and put the momentary switch back on my dash.

Here are some instructions I found. Do they sound correct?

Glow Plug Controller By-Pass
Take the WHITE wire OFF the GP Controller(GPC), and insulate it with tape. ADD a wire from where the white wire had come off, and run it to a Momentary Switch on the dash near the Wait To Start light,
from the other side of the Momentary Switch to a good ground.
Also cut the Blue/White wire going to the GPC and connect
that to the terminal on the GPC where the white wire was attached(you’ll now have 2 wires on that terminal), that will make the Wait To Start light come on when you press the button to glow up the plugs for however long you hold the Momentary Switch.

 

[Diesel JD]

Sounds overly complicated. What I did was pull my purple wire from the fender mount power relay, put a wire from the positive terminal of the passenger side battery, then run a wire of the same size from the relay to the dash, place a 10 amp fuse inline. You want to get a momentary toggle instead of a true toggle switch. It reduces the chance of burning out a set of plugs.

 

[82F100SWB]

If your truck still has the stock setup, what you posted doesn't apply, that's for the 87+ trucks with the solid state system.
All you need to do is run power to the I think purple wire on the relay(it's the one on the engine side of the relay on my truck) through your momentary switch, and to a power source. Personally, I prefer to run an ignition switched source so it only works with the key on the run position. I have a 5A fuse inline with mine, works just fine.

 

[Diesel JD]

Yeah it is the terminal where the purple wire is. You want to take that wire loose and let it hang, tape it up whatever, just don't let it be touching the relay. Hold the glow plug button on no longer than 6-8 seconds at a time consistently, maybe 10 or so in really cold weather. It should start every time like that.

 

[cleithau]

I'm confused, why is the dealship putting a new GPC in if you want to bypass it? Or you just want to run it manually for a few days?

Anyways.....everyones got it right. The purple wire is the one you need to take off. Your wiring should be just like my 1985. If you have eliminated the old water seperator there was a wire running to it that I used as my hot/with the ignition on. I ran that wire to the switch, and the other wire from the switch to where the purple wire was on the GP relay.

Cold weather: out of the book: Factory GPC glow time:

-20F 7-15 seconds
0F 7-12 seconds
35F 5-12 seconds
70F 3-5 seconds

If its below freezing I glow mine for 12 seconds, if its below 15 or 20, I don't know exactly but bitter cold, I glow for 15 seconds. Thats if its not plugged in. If its plugged in I'll glow for 7-10 seconds depending on hold long it was plugged in.

 

[quickster45]

does this work for solid state GPC, or older ones. I have a '91, didn't see any purple wire.

 

[mankypro]

Ok folks help here. Trying to find my glow plug relay. Is it the round object in the middle of the picture with 2 large gold posts & nuts?

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[flexneck]

dude, the thing on the left is most certainly your starter switch.

the gizmo you so neatly circled is the GP relay, yes.

the controller will be on the back of the engine somewhere. i don't know where it is for sure, as my truck didn't have one anymore by the time i got it. but if you have a GPC coming that works, why bother? the trouble with the dash-switch is that you are prone to cook your plugs should one or two fail. if your controller is working, it will shorten the glow-time according to the resistance drop due to the missing plugs. if you have a switch, you just keep glowing and end up cooking the remaining plugs because they were getting too much juice for too long. unless you use continuos duty plugs, but thats most probably not what's in there at the moment...

why do i know this? because i have the evidence, 200$ worth of brand-new dead GP's that i cooked in the course of understanding the finer details of pre-glowing a 86' 6.9L IH.

 

[mankypro]

The reason I'm hot wiring this is because I've had two GPC's fail on me and fry almost all my plugs. My vintage GPC tends to fail in the "on" position.

Make sense?

dude, the thing on the left is most certainly your starter switch.

the gizmo you so neatly circled is the GP relay, yes.

the controller will be on the back of the engine somewhere. i don't know where it is for sure, as my truck didn't have one anymore by the time i got it. but if you have a GPC coming that works, why bother? the trouble with the dash-switch is that you are prone to cook your plugs should one or two fail. if your controller is working, it will shorten the glow-time according to the resistance drop due to the missing plugs. if you have a switch, you just keep glowing and end up cooking the remaining plugs because they were getting too much juice for too long. unless you use continuos duty plugs, but thats most probably not what's in there at the moment...

why do i know this? because i have the evidence, 200$ worth of brand-new dead GP's that i cooked in the course of understanding the finer details of pre-glowing a 86' 6.9L IH.

 

[Diesel JD]

What you said ius true about the 87 and later glow plug systems, as far as shortening the glow time for a failed plug but not for the 83-86 systems which don't even know that the glow plug next to it is there. Each and every one gets 12V and stays on for a set period of time based on the teperature of the control unit. It works awesome until that latching relay stucks in the on position. Some people never have this happen but more often than not, they fail and take most or all of the glow plugs with them. Yes you can cook the 6V glow plugs with a manual toggle as well, but if you keep your preglow time to no more than 8 seconds, ever, you'll keep them many more starts and miles than the factory controller, unless something else is wrong. BTW manky now has heavy duty AC 12V plugs from what he posted in another thread.

 

[flexneck]

oops, i wasnt paying attention and thought we were talking about a '91. with an ?84? there should be no difference between just triggering the relay with a switch or through the controller. but, Diesel JD, now i;m confused...the latching relay that sticks "on", is that the one at the fender or a relay thats part of the controller setup (that i have never seen in real life)?

 

[Agnem]

The factory GPC, which is on the drivers side rear of the engine is what sticks "on". The glow plug relay on the fender, is just as reliable as a starter relay, which is exactly what it is. In fact, the last starter relay I bought was actually a glow plug controller relay in a different box with a different part number. You can use them interchangeably. I'd recommend pulling the harness connector off the top of the glow plug controller (on the back of the engine), and take the controller out and put a pipe plug in the hole.

 

[mankypro]

And one last time because I'm dense:

1. pull the purple wire from the gp relay.
2. run a wire from the battery pos (+) terminal or a ignition on accessory in the cab to the dash mounted momentary switch.
3. then run another cable from the other pole of the momentary switch to the post where the purple wire had been connected on the gp relay.

sounds right?

Reason I'm verifying is because I've had one individual say to run + and another to run a ground.

 

[cleithau]

Thats right.

 

[Agnem]

I'll second that synopsis.