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Is the part near the solenoid labeled "Short Circuit Protection" a self resetting breaker? That would explain the loss of power after attempting to start and it coming back.
That is the voltage regulator. It controls the charging system. As long as the battery is fully charged, the engine would start just fine without it.
I decided to start from the beginning. I didn't have anything at the voltage regulator so I cut open this rubber splice that connects the voltage regulator to the wire you mentioned. I don't know if you can tell from the picture but that wire is cooked. And that's after cutting it from the splice and stripping it back.
Thank you so much to everyone who helped!
That was not a splice. That was a fusible link. It burns up when there is a problem. It's a undersized piece of wire with special fire retardant insulation around it. You can get by without it, but it would be nice to replace it. Obviously the truck was running, you did something and shorted something out, and it burnt the fusible link. That is why it's nice to have it.
P.S. Re-reading your first post, I would guess you had a battery problem or a connection at the battery. But in the process of troubleshooting the fusible link got blown. The easiest way to blow the fusible link is to put the jumper cables on backwards.
Last edited by Franklin2; Mar 1, 2026 at 03:32 PM.
I found the problem was a factory splice that went bad.
Making progress, but I hate to rain on your parade. That wasn’t a “factory splice” that went bad for no reason at all. It was a fusible link, basically a glorified last chance fuse built into the wiring harness. The circuit was overloaded and the fusible link responded exactly as designed.
If you replaced that fusible link with regular wire, the original fault is likely still present but now the protection is defeated.
Making progress, but I hate to rain on your parade. That wasn’t a “factory splice” that went bad for no reason at all. It was a fusible link, basically a glorified last chance fuse built into the wiring harness. The circuit was overloaded and the fusible link responded exactly as designed.
If you replaced that fusible link with regular wire, the original fault is likely still present but now the protection is defeated.
Are you sure that was a fusible link? The electrical diagrams don't mention one there, it doesn't look anything like the other fusible links, and it didn't have a rating on it.
Edit: I just checked and all the other fusible links are rectangular and are marked "fusible link x amps". If this is supposed to be fused I'll put an inline fuse there but since nothing is marked I wouldn't know what size fuse to use.
Well, it’s difficult to be sure from many miles away.
Where exactly was this wire connected? Did it have a large ring eye terminal? Was it connected to the starter relay, at the big terminal with the short heavy cable going to the battery’s (+) terminal? That terminal is used as a convenient junction post to feed battery power to all circuits. All of the wires connected there are fusible links.
I also have an 81 F250. My starting and charging circuits were butchered by a previous owner, so I've made a science of how Ford originally wired that truck. I'm attaching a complete schematic that I pasted together from multiple pages. It is accurate, schematically. It may take some effort to find where some of the connections actually happen, but you can trust the diagram.
One commenter mentioned that all the ring terminals that go to the hot post on the solenoid are fusible links. He is correct, except for the black/orange wire to the EEC power relay. Trust the diagram.
2 of them on my F250 had been eliminated. I put new ones in. Endeavor to keep everything the way Ford designed* it. The engineers Fomoco hired were good. They knew what they were doing. Don't F' with their work. Trust the diagram.
* I typed "designed" on purpose. Sometimes, changes got made on the factory floor, and those changes often were not approved by the engineers. The results were sub-optimal. Trust the diagram.
Yellow to voltage regulator, left black to starter solenoid battery terminal, right black to alternator, and red to this:
That harness goes here where there are fusible links:
If you zoom in on the first picture you can see that the wires are just pressed together.
One commenter mentioned that all the ring terminals that go to the hot post on the solenoid are fusible links. He is correct, except for the black/orange wire to the EEC power relay. Trust the diagram.
Thank you. I can't zoom in enough on your diagram to read the colors. When you posted this I was posting some pictures. Can you look at them please? If it is supposed to be fused can you tell me how many amps?
I’m looking on my phone so it’s a little tricky to fully understand where this wire is located. Maybe someone more in the know can help.
One possible point of confusion: The fat rubber splice is not the fusible link itself. The fusible link is a short length of undersized wire with special flame resistant insulation.
The fat rubber splice is only the splice or coupling. If the fusible link is in the middle of a wire run (not very common) it will have the funky splice at both ends. If at the end of a wire run (more common), such as at the starter relay junction, you’ll only have one splice. The other end of the fusible link is crimped directly to a ring terminal.
If a fusible link has been previously replaced, it will have a more standard type of crimped connector(s). I think those fat factory splices were used to help identify the fusible links.
Your posts and the the info on here is getting better.
It looks to me that your AMP METER has been converted to a volt meter.
Info and photos in the link below.
An amp meter will have the needle in the middle of the gauge, at rest, no power.
https://www.ford-trucks.com/forums/1...olt-meter.html
It looks like there's a "extra" relay, just aft of the starter solenoid. Is the connection to the red wire? Possibly for the volt meter conversion??? Reference post 23 , photo 2
I will post a photo next of what the fuseable link / splice looks like in its original condition.
Jim
Last edited by JimsRebel; Mar 1, 2026 at 07:30 PM.
This is a 1986 2G alternator truck, but very similar to what you have.
The round black thing, is just a rubber protection for the splice under it.
The actual fuseable link (wire) is between the splice and the ring connector.
The yellow wire exiting the spice goes to the voltage regulator.
The green wire, far left in photo, also goes to the voltage regulator.
The small red and yellow wires exiting the 4 wire connector (plug) are used for the amp meter originally and also reused if you have a volt meter conversion.
At this point you have no protection (fuse) , a 30 amp might blow as it might be to small, but it would be a starting point.
The actual fuse box load would be less if you have headlight relay, keeping the amp draw out of the cab. Headlight relays are one of the best and easiest modes, highly recommend.
Jim
Last edited by JimsRebel; Mar 1, 2026 at 07:24 PM.
The round black thing, is just a rubber protection for the splice under it.
The actual fuseable link (wire) is between the splice and the ring connector.
At this point you have no protection (fuse) , a 30 amp might blow as it might be to small, but it would be a starting point.
The actual fuse box load would be less if you have headlight relay, keeping the amp draw out of the cab. Headlight relays are one of the best and easiest modes, highly recommend.
Jim
Thank you. If an inline fuse might blow can I buy a fuseable link? What amperage should I be looking for?
Edit: I'm unsure what that relay is. The schematics I'm looking at show a marker light relay that could be there. I'll check in the morning.
Maybe orange, color code.
Do you have anything of the original one, color wise
Not really sure, I never have changed one.
The Auto parts store sells them.
Maybe someone else knows the correct size for you truck.
Are you still using the original ford 1G alternator?
Jim
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