GP Controller
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Junior User
Joined: Oct 2010
Posts: 81
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From: Norfolk
I have found the wire that activates the starter solenoid, I just dont have power to the GP controller when I am in the start position. Its fine when it is in the run position. Am not worried about the controller as much as the fuel solenoids de-activating when its in the start position. Any suggestions as where to look? This truck is really trying my patience. 
Senior User
Joined: Mar 2010
Posts: 419
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From: Timmins, Ontario, Canada
Oh I see, you're cutting off fuel while starting because the FSS is powered through the post on the GP, which isn't wired for both start AND run...
Take a look at the first schematic I posted, (27-3).
What you need to do is find the circuit in your engine compartment fuse box that is on in start and run for the GPs (originally slot K) and wire from there to the GP relay, then from the same post to the FSS.
To check that wiring, pull open the engine compartment fuse box on both sides (open the top door to see the fuse slots and pop the clips on the bottom to access the wires running to each fuse) and test for voltage there. If you have no voltage in there, I'd have to look at the power distribution schematics again, but I could tell you which IS wire routes voltage from the batteries to the engine compartment fuse box.
Don't give up on this truck! It may be a mess right now but its a tribute to the engine's simplicity that you've seen pretty much the whole engine electrical system just here. No computers to mess with!
Take a look at the first schematic I posted, (27-3).
What you need to do is find the circuit in your engine compartment fuse box that is on in start and run for the GPs (originally slot K) and wire from there to the GP relay, then from the same post to the FSS.
To check that wiring, pull open the engine compartment fuse box on both sides (open the top door to see the fuse slots and pop the clips on the bottom to access the wires running to each fuse) and test for voltage there. If you have no voltage in there, I'd have to look at the power distribution schematics again, but I could tell you which IS wire routes voltage from the batteries to the engine compartment fuse box.
Don't give up on this truck! It may be a mess right now but its a tribute to the engine's simplicity that you've seen pretty much the whole engine electrical system just here. No computers to mess with!
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Junior User
Joined: Oct 2010
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From: Norfolk
OK, have found the fuse slot that is both hot on the start & run position. But as I was headed there, taking out the headlight switch to get to the wires i needed, have found that the headlight switch connector is melted and broken, plugs falling out of the connector, loose wire floating around backside of switch, hot 1's at that. Probably will have to go back to the JY for that. Also the fuse box is missing wires, glad there is only an under dash 1 in this truck. No PDC in the engine compartment on this year. Thanx again for all yer help northern, you have been an enormous help to me on my 1st 7.3 adventure,( gotta call it something so it might as well be an adventure). Will keep everyone posted as to how this is going!!!
Senior User
Joined: Mar 2010
Posts: 419
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From: Timmins, Ontario, Canada
Oh man, sounds like that truck was treated like crap, but good to hear there's some progress!
The main light switch, the starter motor and the ignition switch are the three places battery power runs to - absolutely everything else flows through there, so that's a good find to fix first off. Good luck with it!
The main light switch, the starter motor and the ignition switch are the three places battery power runs to - absolutely everything else flows through there, so that's a good find to fix first off. Good luck with it!
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Junior User
Joined: Oct 2010
Posts: 81
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From: Norfolk
Ok all, from 1 dilema to another. I went to the JY and got the connecters I needed. Put them all in, did a pelimanary check before I put the dash together, everything worked(whew!). Then I hooked up the light switch, finished the lower dash, and then nothing. I have power to the GP on the starts side, but not on the run side of the IS. Started checking wires, and now the ignition wire to the GP controller is making continuity to ground. I am getting frazzled at this thing, think I might just go find a wrecked truck & pull the whole wire harness for the cab & engine compartment. I have power to the fuel heater, starter solenoid, altenator, and all other area's, just not the GP controller. Any suggestions as where to look? Any ideas would be a great help!
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Joined: Jul 2010
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Bluesman, not sure if this will help or not but I have a 90 F350 with IDI 7.3 diesel. Mine would not always stay running after starting when the key went back to the run position. It was intermittent for a while and kept getting worse. I had to hold pressure on the key switch to keep it running after starting. I finally broke down and tore into it to see what was going on.
What I found was the ignition switch down on the steering column was seperating from the metal base that bolts on. In fact as I was trying to take the cannon plug off the switch, the thing just came apart. Anyway what was happening when the key was going back to run, the switch contacts were not close enough to make good connection. I put it all back together and tightened up the four little prongs on the metal part of the ignition switch so there was no longer a gap between the base and contact portion of the assembly. It works great now!
Not sure if this helps but you saying that you are loosing power now in run when you had it before. Well at least I think you said you didn't have it in start position when you first started this thread. Keep at it, you will get there.
What I found was the ignition switch down on the steering column was seperating from the metal base that bolts on. In fact as I was trying to take the cannon plug off the switch, the thing just came apart. Anyway what was happening when the key was going back to run, the switch contacts were not close enough to make good connection. I put it all back together and tightened up the four little prongs on the metal part of the ignition switch so there was no longer a gap between the base and contact portion of the assembly. It works great now!
Not sure if this helps but you saying that you are loosing power now in run when you had it before. Well at least I think you said you didn't have it in start position when you first started this thread. Keep at it, you will get there.
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Junior User
Joined: Oct 2010
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From: Norfolk
Morning All. I have had to take a few days away from my 7.3 project. I am headed back in today to see what more mess I can find. I am gonna try to get it running with all the lights and acceseries disconnected. If that works, then I am gonna replace the whole trucks wiring from another truck, so I will keep ya'll posted on this wiring nightmare. Thanks again to all who have helped me on this project.
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Junior User
Joined: Oct 2010
Posts: 81
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From: Norfolk
Ok, got power back to the controller, with the rest of the dash wiring disconnected(mostly the lights). My new glow plugs should be here today or tomarrow at the latest, am anxious to hear this 7.3 run. Then it will be off to the JY's to see if I can find a complete wire harness for this rig. Maybe someone on here may have a wrecked 89 with a 7.3 they would be willing to part with the complete chassis/cab/engine harness. If so please holler at me, cant seem to find very many trucks with this engine in the area I am in. Thanx all!!!
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Thread Starter
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Junior User
Joined: Oct 2010
Posts: 81
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From: Norfolk
Ok all, I finally got it to fire up. But now I have to do a tear down, got water in the oil. Gonna do a comp. check to isolate which clynders are bad and see from there. Looks like this truck is gonna make me earn my pay,lol. Just havent figured I would have to go this far, but so be it. Think I will wait till I get back from vac. before I start. 2 weeks in the Adirondacks should get me rested enough for the next phase. Thanx again to everyone who has sent me advice, I do appreciate it very much. Will keep ya'll updated when I've had my fill of trampin thru the woods lookin for dinner!!!
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