Let me start by saying that I'm new to the Forum and I appreciate the help from you guys. I've already learned a vast amount about these trucks just by casually browsing around. This is an invaluable resource!

To my issue:

I come across a '94 F-250 EXT Cab LB w/Banks Sidewinder Turbo from a friend of mine that had given up on it. He was not very mechanically/electrically inclined and figured he'd get rid of it rather that attempt to fix it. The odometer is registering 283k, but from what I was told the motor was replaced in the last couple of years and and less than 60K (unverifiable) on it.

Anyways, who ever it was that replaced the motor made a hell of mess of the electrical system which is why he couldn't get it to start.

I had to "Jump" power to the GP Relay in order to start the motor. When I do this I hear relays clicking elsewhere which I presume are the fuel solenoids for the mechanical pump. When this is done the truck cranks up and runs great, however this also is rendering my tachometer inoperable, so I am getting the confused E40D tranny not starting or shifting gears correctly.

When the GP relay isn't "Jumped" they motor will turn over all day, but will NOT run. The odd thing though is when GP relay isn't jumped the Tachometer will correctly read as the motor is turning over.

I need help straighting out the ignition wires that should be doing the job of turning on the pump solenoids and GP relay and at the same time keep my Tachometer operating.

The way this truck is currently wired, they ignition switch is only good for cranking over the motor. Without first jumping power to the GPR, the motor will only turn over, and the only way to cut off the Engine is to remove the Jumper wire for the GPR. Turning the switch off does nothing.

I apologize that this so long, but I wanted to provide as much info as I could.

Your Thoughts?

AB

 

It sounds like sometime the injector pump solenoid got wired into the GP relay wiring. The injector pump should have power any time the key is forward, whether for crank or run. The glow plugs only need power when the motor is being prepared to start, no other time. Somebody must have decided the GP's need to be energized all the time... (I have been told that they are what makes the diesel fire....)

 

The ignition circuit goes many places.
Most of them are on the passenger side inner fender.

Red wire with a green stripe goes to the voltage regulator and into the harness going to the engine.
Once on the engine, one branch goes to the ignition terminal of the glow plug relay, rear of the intake manifold.



Going to the front the wire splits again, one goes to the coolant temp switch down by the thermostat housing.



Power in on one terminal and out on the other when the coolant temp is under 112 degrees.
The out wire goes to the timing advance solenoid and high idle solenoid on the injection pump.



The other wire that split off before the temp switch also runs to the injection pump to the fuel shut off solenoid.
And there is one more branch that runs to the fuel heater connection located on top of the fuel filter header.

So if the engine is cold when you turn the key to ON, the fuel shut off solenoid, timing advance solenoid, high idle solenoid, fuel heater and glow plug relay ignition terminal should all have power.

When the engine is warm and the key is on, you should have power to the fuel shut off solenoid, fuel heater, and ignition terminal of the glow plug relay.

The glow plug relay works by supplying a ground to the trigger circuit through the white wire from the controller under the relay if you are wondering why it always has power.
Also the battery terminal wires run straight to the battery positive terminal, so be careful when working around the relay, big sparks if it gets shorted.

 

Thanks for your assistance Dave. Tracing these wires and getting it hooked back up as they were intended will be my project for this coming weekend.

My guess is that when all this re-wiring was done, that one of the wires for the tach sensor got crossed up with it. That the only way I can figure how the tach will work when all this other stuff isn't manually "jumped" on.

 

fuel heater is always on? even when vehicle is warm???

 

Check the wiring on the right fender...... look for a large black plug with black/red wires....near the rear......... That plug will burn up and no power goes anywhere. Just remove the wires from the connector and solder them solid cover with heat shrink.

If you do not have that black plug look for the Grey plug with yellow wires and do the same thing... I don't remember which is what year....... sorry

 

There is power to the fuel heater, but it only operates at temps below 32 degrees.