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I have a 1990 F800 with 6.6 brazilian engine and need some ideas and assistance with this older boom truck. The solenoid that shuts down the fuel was not working so I replaced it with a new solenoid. Unfortunately, I have the same problem that the solenoid is not actuating in run, but does in start.

The truck runs if I use bailing wire to hold solenoid down, ( fuel is on) although I have to dump the clutch in high gear with brake on to kill engine.

There are three wires going into the solenoid. From what I can figure out, one is the ground, one is for the start circuit ( I assume full voltage), the other is for the run circuit ( I assume less than full voltage). I have power to the start wire, so the engine tries to start when starter is moving. When you turn key off of start to run, the engine dies. There is no voltage to the run wire heading into the solenoid. I have tried following the wire back up to fix the problem, but it goes into large bundles that I really don't want to cut into if I don't have to. It appears that run wire is serviced by a T connection going up to alternator (red wire with blue stripe), and appears to have maybe a hard 3" long resistor in the circuit . The other end of the wire goes somewhere back into a large bundle that goes toward top of engine.

Questions: Any wiring diagrams out there for a 90 F800? Might help to understand what the circuit should be to compare to the bastardization I have now.

Should the "run" wire to solenoid have less voltage (like in points for a car - full voltage to start, resistance wire to lower voltage to run)? I was thinking of just bypassing the wire to something else if nothing else.

The alternator is a napa and has two wire plugs that go into the unit. 1) a three wire bundle, 16 ga wires, with the red wire with blue stripe and two others. 2) other plug has three wires. Two large gauge, power out I assume plus a smaller ga white wire with black stripe. Need to look to see if voltage regulator is separate on fender (most fords) or internal to alternator.

I checked all the fuses and they are ok.
Thanks for your help in advance.
 

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Perhaps this might help.

Pull the plug, and attach a multi-meter to each socket individually.

I have a Deere 844 loader with a similar 3 wire solenoid. While I took mine off and installed a cable operated unit, I checked my wiring first.

It took me a while to understand why but mine read as follows....

Black wire - ground
White wire - 12v
Yellow wire - 9v

Deere uses a different approach, but in hindsight I could have rearranged the wires in the socket and tried to get it to work.

Also if you know the manufacturer of the replacement solenoid, you can usually call them with the part number and get specifications on that part.

Sorry I couldnt be more help.
 

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I have a 1990 F800 with 6.6 brazilian engine and need some ideas and assistance with this older boom truck. The solenoid that shuts down the fuel was not working so I replaced it with a new solenoid. Unfortunately, I have the same problem that the solenoid is not actuating in run, but does in start.

The truck runs if I use bailing wire to hold solenoid down, ( fuel is on) although I have to dump the clutch in high gear with brake on to kill engine.

There are three wires going into the solenoid. From what I can figure out, one is the ground, one is for the start circuit ( I assume full voltage), the other is for the run circuit ( I assume less than full voltage). I have power to the start wire, so the engine tries to start when starter is moving. When you turn key off of start to run, the engine dies. There is no voltage to the run wire heading into the solenoid. I have tried following the wire back up to fix the problem, but it goes into large bundles that I really don't want to cut into if I don't have to. It appears that run wire is serviced by a T connection going up to alternator (red wire with blue stripe), and appears to have maybe a hard 3" long resistor in the circuit . The other end of the wire goes somewhere back into a large bundle that goes toward top of engine.

Questions: Any wiring diagrams out there for a 90 F800? Might help to understand what the circuit should be to compare to the bastardization I have now.

Should the "run" wire to solenoid have less voltage (like in points for a car - full voltage to start, resistance wire to lower voltage to run)? I was thinking of just bypassing the wire to something else if nothing else.

The alternator is a napa and has two wire plugs that go into the unit. 1) a three wire bundle, 16 ga wires, with the red wire with blue stripe and two others. 2) other plug has three wires. Two large gauge, power out I assume plus a smaller ga white wire with black stripe. Need to look to see if voltage regulator is separate on fender (most fords) or internal to alternator.

I checked all the fuses and they are ok.
Thanks for your help in advance.
did you figure it out i have the same truck and issue??
 
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