I have a 1985 f250 6.9idi and it won't start. My problems began a week ago when the frame solenoid went out. So they're cheap and easy to replace so I did. After installing the new one I still had to jump the solenoid to get the truck to start. Is there another solenoid I need to replace? Before today I had to turn the key to the glow plug position and then jump the solenoid. Now today the battery was dead after I was out hunting so I got a friend to jump start it. Got down the road and the eng temp and oil pressure gauges starting going up as I stepped on the accelerator. I thought that was weird so I pulled over, shut off the truck, and checked under the hood. Everything looked fine, but when I went to start it back up none of the electronics worked. The cab light wont come on, glow plugs aren't turning on, turning the key in the ignition does nothing now, nothing electrical is working now. I can jump the solenoid and the engine turns but it wont start. Any ideas on what I should start looking at? The batteries and alternator are only 6 months old.

 

This sounds like the Ignition switch, or related in some way. If the Key Switch is doing nothing, then that is where to start looking. Also, Auto or Manual, could also be a shot Neutral Safety or Clutch Switch.

Also note, the Gauges in your dash rely on Resistance to work properly. They are not a Voltage based system like your Cruise Control or the lights on your truck. This means the two systems, even if directly connected would and should just short. There is not Computer per say on that truck at all. The wiring for the starting sequence goes as follows. Key turns switch, switch sends power through the resister wire to the Fuel shutoff switch and glow plug controller to determine if glow plugs are needed. Then if you turn to Start, which throws the Ignition switch (at the base of the steering column) then power is sent to the Neutral Safety Switch which allows or does not allow starting based on the position of the center shaft in relation to the pins inside. (is it in Neutral or Park) This is a common failure point, they are cheap now and made of weak plastics. If a manual then there is a similar device that works of if the Clutch is engaged or disengaged. Then the power makes is last leap, where it has to trip the Solenoid on the Fender. This either gets enough Voltage to trip and send the power to the Starter, or it does not. This is another common failure area, but ultimately that is the last leap in power. At that point power is going to the ONLY TWO locations that are technically needed for that truck to start. Fuel Shut Off Switch and Starter. Nothing else is required, even in cold temperatures you can start without Glow Plugs, so the dead circuit in my opinion has to be in the ignition switch area. The Gauges are again on a separate system, so they shouldn't (With electronics... anything is possible) interact at all. If they did it should have nuked your dash.

 

Thank you for the reply, Vegetable! I'll start at the ignition and work my way down the chain you described.

 

Did You find out what the problem was Jason?
I've got 2 86's but when they haven't started in the past it's turned out to be a slough of problems.
Main thing I've learned is to have 2 badass batteries to start these old beasts and I've gotta charge my batteries about once every 2 months on the 4x2 but my 6x6 has a short somewhere so I take battery cables off batteries every time i park it. Got to where i let hood click into first latch but wouldn't shut it all the way due to frequently opening to connect & disconnecting batteries. Hood hasn't flown off at 80mph yet haha