complete power loss for 85 f-250 diesel
 

i am a proud owner for a 85 f-250 diesel 4x4 with an automatic transmission. it has 167,000 miles on the odometer. it runs very good. but the old ford had a problem. it will flat out and stall with no warning. there is no power anywhere. no lights wipers, no nothing. but let it sit for a couple of hours and the power is back on and runs fine. i'd like to believe it's the alternator. but when i have it bench tested. it passes every time.

What engine do you have, and what is going on when it just "flat lines" on you? what I mean by that is do you hit a bump, or what?

A buddy of mine had a bad connection in his fuse/relay box under the hood, and it caused it to just die, and then start back up later. I'm not saying this is your problem, but giving an example.

When this happens, do the headlights work?

Vertrees is on the right path, the power feeding the cab comes from the wires and fusible links connected to the battery side of the starter solenoid so that's where I'd be looking.

If your location is because of a career, appreciate your service OP.

AFAIK the diesels are not subject to the heat related ignition setups the gassers had.

But, if the cutout is not bump related, is it heat related? An old trick is to get a very good hair dryer, or preferably a heat gun, and use that to heat parts in the wiring track Chris is talking about before the engine itself warms up. If you heat up a junction or relay and it cuts out before the truck is warm, there you go.

There's a couple tool stores around me that rent them. Also, Harbor Freight had one on sale for $20 a couple months ago.

the old ford flat lines. there is no power anywhere. honestly it's like the batterys just go dead. i've had the batteries checked right after it happened the second time and the local parts house said there fine. along with the alternator. i did also replace the voltage regulator. my dad said it maybe the amp meter.
i'm a need on help. please any ideas.

They have already pointed you in the right direction. Over on the passenger side inner fender is a relay like every Ford has. On the diesel they use this to activate the starter(the start current doesn't go through it like a gas truck though) and like the gas trucks, the factory uses this spot(one of the large posts on the relay) as the main point to pick up 12v to run the whole truck. There is usually a yellow wire(since it's a diesel you may have more than one) with a fusible link, and this leads to a splice which where it then goes to the alternator, and to the under dash area where it hits the ignition switch, and then keeps going to the fuse box.

Since this is an intermittent problem, what I would do is look everything over and get a idea whats going on, and look for obvious problems(you may have to unwrap some of the harness. If you see nothing, I would get some 10 gauge wire and hook one end to the starter relay power point, install a circuit breaker inline, and then hook the other end to the yellow wire under the dash where it goes into the ignition switch. If the problem goes away, you know the problem is between the ignition switch and the starter relay.

Usually though, just poking and messing around with it, you will stumble upon the problem by accident.

Also, check the ring terminals on that fender mounted solenoid. They can get corroded leading to this type of issue.
It almost has to be somewhere in this portion of the wiring. Loose power to the ignition switch, and it cuts the power to the shutdown solenoid on the injection pump. Engine dies, and all electrical does too.

I had the same problem last summer, on the right inner fender there is a yellow wire that supplies power to the cab, I goes from 1 yellow wire, to a gray connector, then splits into a green one and orange wire. That gray connector is probably causing your issue, it gets warm and builds resistance until it breaks contact. Replace the connector with a heavy splice or solder the wire together.

That's the same problem I've had in the past and there was another thread recently about this. That stupid connector isn't sealed, so water works its way into it, corroding either the pins or where the pins are crimped to the wires. Pull it apart (if you can) and check for green.

Mine was getting so warm I could mold the plug into cool shapes with my fingers.