Well on the way home from the lake yesterday, had a mishap and trying to trouble shoot.

Someone had installed a capillary tube oil pressure gauge and unfortunately somehow it shorted out.

Sequence of things were as follows, short on firewall, eventually broke the tube to the oil pressure gauge, spewing oil all over the driver side exhaust manifold., small oil fire, put out very quickly, but all of the gauges spiked, radio quit working and the glow plug light came on and stayed on, the real odd one, was could not shut the truck off with the key. To turn the truck off, so it did not grenade, I pulled the power lead from the fuel injector solenoid.

Now, if I hook the batteries up, the only thing that gets power is the glow plug light, which continuously burns, but no power to anything else in the truck, I only found one burnt wire and that was the ground wire that is attached to the wiper motor, spliced it back together, no change.

One other thing I did yesterday, was to pull all of the fuses and circuit breakers out and the glow plug light still stayed lit. So after a bit of reading, I figured it was probably the ignition switch located on the column, I took it out and apart(going to replace) but wanted to see if anything was burned, nothing in the switch showed signs of shorts and nothing in the wiring behind the dash is burnt. One other thing, when I checked the fuel injection solenoid, even with the key off, but the batteries hooked up, there is power on that circuit, so I know something is fused somewhere allowing direct power.

So now I am in a conundrum, with nothing but a ground wire showing signs of the short, I am at a loss to what circuits would cause the truck to continue to run with the key off as well as keep the glow plug light illuminated.

As my title says, it is an 1985 F250 6.9 IDI, with automatic and an aftermarket ATS turbo system on it, ran great before this mess and I just installed a new 5th wheel hitch to tow our trailer, so would really like to get this back to working order ASAP, I will be replacing the ignition switch after work tomorrow, but figured it wouldn't hurt to ask here, I have followed this page for over a year now and learned quite a bit.

Thanks in advance for any help you can provide, I am a pretty good wrench, but not as familiar with the systems in these old diesels.

Dave

PS, Just a bit of an update, I just checked the power at the injector solenoid and even without an ignition switch in the vehicle it is getting power as is the glow plug light.

 

Hmmm,

No Ideas from Anyone?

 

I'd guess that some wires melted together somewhere and it is feeding power into another circuit.

 

The electrical system is fairly simple on these trucks. If I can figure mine out anyone can lol. How does the main harness through the firewall look. Every relevant Wire passes through there. And on the driver side by manifold you have that plug. I'll peek at mine tomorrow and check. See if any lightbulbs click

 

The truck not turning off is not the ignition switch, it is a grounding issue. I'm guessing some wires were melted in the fire and are supplying voltage to each other and or grounding inappropriately. As for the gauges, they work on resistance.. The higher the resistance the higher the reading. Therefore, if you have an open circuit, the gauge will peg. As with the previous post, take a poke around where all those wires go through the firewall.. One loose, burnt or grounded wire (that shouldn't be grounded) can cause so major symptoms. As you already know.

Oh! And pay particular attention to where the wires to the new gauge are tapped into your system! Good chance something was not done correctly..

 

Well, have made a bit of progress, I did the multimeter test this evening and did find a draw, the way I tested, was disconnect the ground, hook the red lead up on the meter, then the black lead to the battery negative post, did not register on the 10 A range, but showed an overload on the 300 Milliamp range, and found where the harness goes through the firewall, so will split the tape on that bundle and find which wires have been compromised. I am thinking this was probably more than the copper capilary tube that caused the problem, but I am going to reinstall a new pressure sending unit and hook the dash gauge back up for the time being, which should be fine.

I know these old diesels don't require much to run, but this one flubbered me for a while.

Thanks for your help, I will update when I get it running again.

Dave

 

Alright I figure if you undo The firewall harness and see if you still have the the glow plugs on with the key off. That will tell you if it's under the hood or under the dash. If the problem goes away the short is under the dash. If not it's in the engine bay harness. Hope that helps

 

Trace all of your wires. With what hot oil spewing, you must have some melted up wires. If you find small spots that are bad, you can cut them out and splice in small replacement sections of wire. If you do that, just make sure you solder everything and use heat-shrink.

 

Well it looks like I have found the problem, found a ground wire, that was swelled up, the bolt it connects to, show a direct short, but the wire has no continuity through it, so it looks like it burned off inside the shield with little indication of it going bad, should be able to build a new one and replace(easier said than done) and be back in business, then put everything back together I had to take apart to find the darn thing!

I put a new ground wire on it today, and now the body does not show current going through it, but when I hook up the batteries, it shows a heck of a short somewhere, so now that I have the faulty ground wire fixed, I can actually see if I can find the short in the harness.

 

Well after restoring the burnt ground cable yesterday, as I said I had a big direct short, so doing some testing this morning, I carefully hooked one battery and had a small puff of smoke as well as the sparks looked like a welder, started tracing wires and low and behold, the large positive cable going from the drivers side battery to the passenger side battery had fused into the radiator support, causing a direct short to the body of the truck, pulled it away and low and behold everything started working again!



Thanks for the help guys, I know one thing, it sure taught be a lot about these old diesels, and really how simple they are! Took me all afternoon, the put the darn thing back together!

 

Nice work! That same battery cable on my truck is starting to crack open as well.. I'll definitely have to keep an eye on it, especially after reading your results. Thanks!