Slowly working to get my 91 F250 7.3 IDI running again after it sat for 8 or so years. Here is a link to my original intro thread on this forum regarding that truck

I am sorting some wiring issues out and have found one wire at the starter solenoid that seems to splice two wires together from the harness and power them both at the solenoid. After referring to some photos of other 7.3 IDI engines I have the idea that these two wires are supposed to be bridged together and powered by the positive side of the solenoid but were at one time part of a single fusible link. Can anyone confirm this?? Attaching a couple photos. The wire I'm referring to is the greenish one extending from the right side starter relay terminal toward the bottom of the image. It powers what looks like a large black wire with orange stripe (alternator???) and a smaller yellow wire (no clue what it goes to).

Also there is an additional red wire that is attached to the same right side starter relay terminal that powers something in the forward harness that travels along the radiator support. I'll try to get some better photos of it at a later date and figure out what it is for, but it too looks like an add-on for something that burned up years ago. Can you guys think of anything else that is supposed to take power from the starter relay??

 

no ides what the red wire is, but i would disconnect it if it is not connected to anything on the other side.
and the green wire does indeed look like a repair for burned out fusible links.

 

After spending some time with the multimeter today it seems both the red wire and the green wire in my photo are items that were at one time connected to fusible links.
There is a small yellow wire that appears to send power to that silver box bolted to the wheel well. The box has a connector with wires that go to the alternator and possibly the AC compressor or maybe the 2-wire sensor that is at the front top of the motor. Does anyone know what that silver box is for? It says "short-circuit protected" on the top of it.

 

that is the voltage regulator. it keeps the alternator from overcharging the battery

 

Thank you for your help. By any chance can you confirm that the black/red alt wire is supposed to merge with the yellow voltage regulator wire via a fusible link and then attach to the power post on the starter relay?

 

sorry, i don't have wiring diagrams in my manuals.

 

there are 3 circuits with fuseible links, one powers the truck, one is the charge wire from alt, and one is power to the high current side of the glow system. all should attach to the post of the starter solenoid.

 

In case anyone is trying to diagnose similar issues with their truck I finally got to the bottom of my wiring issues in this thread. The green wire and red wires were put on by somebody presumably to replace burned fuse links but they did a terrible job.

The green wire in my photo is supposed to be a thick gauge wire powering the alternator. Black with red stripe I think. It is supposed to join with a single wire from the voltage regulator, possibly two, and then run through a fuse link to the solenoid. I replaced that whole green wire with a section of original fused alternator wiring from a 6.9 parts truck. Be sure to use the same gauge wiring as the alternator uses, because it is under heavy load and will get very warm. That green wire was too hot to even touch when the engine was running, it's a wonder it worked at all.

The red wire in my photo was also a hack job. It was a power wire from the solenoid to the starter switch on the column. It wasn't the main power wire for the switch, but it was a key part in powering the glow plug system at the starter switch. It didn't have continuity, even though it visually looked connected, so when I turned the ignition key, nothing happened. A multimeter helped me determine that it had an internal break.

If you have issues with your solenoid wiring I encourage you to get a multimeter, some extra length of testing wire and learn how to probe for continuity. I had to feel my way through it, search for some wiring diagrams and watch a couple YouTube videos but I can now say I know the function of the most important wiring running through the truck.