03' 7.3 No Electrical Power

[REF]

Exactly^^^
What you are describing is a battery switch, it can either select one, combine both batteries or shut them off.
I’d also get another new matching starter battery,
Check your fuses, both under hood in the distribution box on the drivers side and under dash on drivers side, make sure they’re all seated properly.
Another culprit could be the PCM, a scan tool will show if there’s proper communication with the PCM(power train control module) and functional.
Also check for a bad CPS(cam position sensor). Usually you’ll just replace this to see if it’s the culprit. Symptoms are the van would crank but not start, so the fact that it starts at all might rule this out.
Another is the UVCH(under valve cover harness). I just had one go out on me while down in Baja, an interesting ordeal. Typically, either one or more cylinders or an entire bank would go down, leaving you to run only half an engine, but it would crank and fire up, sounds and idles rough with little to no power at throttle input. If both UVCH are shot, you might experience your symptoms, but doesn’t really explain the dead dash, that could be an alternator issue, have you checked your alternator output? It’s possible you have a fried diode and it’s causing back charging issues on your batteries.
Could also be a bad, frayed or shorted wire harness.
Have you checked or changed your fuel filter lately? Hiding behind and under the air intake box, it’s the round black cover.
I’d try to get a reputable diesel shop to take a look, they should be able to diagnose.

[arctictraveller]

What you need is a volt meter and a wiring diagram. To me is sounds like a bad connection that allows power to flow until you place a big load on it like the starter motor. I forget what year and model you have, but we traced a similar problem on REF's 7.3 to a bad fuseable link. We found the problem by looking at the wiring diagram and discovering that power to the main fuse block is supplied by the fusable link, located on the fender well on the passenger side, probably under the battery. The point is, with a volt meter, you should be able to find where power stops flowing while everything is dead, but should be powered up. Starting at the battery, you no doubt have good voltage. Working from there to the fuse block, each location to test voltage will be either good or bad. Do you have a volt meter and wiring diagram? I gave away my 7.3 manuals when I sold my SMB, but I do have an older one. If you have a meter, I can help you trace the circuits, and i'm betting you have a bad connection somewhere between the battery and main fuse block that allows voltage to flow until you put a bigger load on it.

[arctictraveller]

The items you mentioned not working are fed from the battery junction box, which in turn are fed by the fusable link attached to the starter relay. Using your volt meter, check to see if there is voltage at the junction box and then at the starter relay (on the passenger side bolted to the fender well) That's the big picture, from there you can begin to test individual circuits if that one is good............

[clicker44]

Awesome!! @arctictraveller thank you so much. And thanks everybody else for taking the time to respond. I am highly optimistic that my issue is the fuseable link. I will report my findings.

[REF]

Ahh....now why didn’t I think of that!

[arctictraveller]

Originally Posted by clicker44

Awesome!! @arctictraveller thank you so much. And thanks everybody else for taking the time to respond. I am highly optimistic that my issue is the fuseable link. I will report my findings.

It's just a guess based on somewhat limited information. The volt meter will be your best friend when trouble shooting. Best of luck........

[7oaks]

I know I'm coming in late on this one but I had the same problem with my 2002 7.3. It would start intermittently and most of the time not at all. Turns out it was weak start batteries. My solar charge system was masking the problem as it would start late in the day but not in the morning. My mechanic determined the problem when he noticed the dash lights filckering when in start mode. He says the 7.3 requires a minimum voltage and current to start. You may have the voltage but it will drop suddenly when the glow plugs come on, may turn over slowly but will not start. Like everyone suggested replace that battery under the hood and check voltages as Arctic suggested. The indicator on this problem is the flickering dash lights. My mechanic found this exact same problem based on flickering dash lights on an F250 right after he fixed my van.

[7oaks]

I just reread the posts and found you already replaced the other start battery. I agree with Arctic the most likely cause is the fuseable links or another open electrical circuit somewhere. You should be able to trace it with a volt meter and following the circuit diagram.

[clicker44]

Update! -- Thanks for the help everyone. The problem has been solved! Starter solenoid was basically melted at the negative terminal. New solenoid and problem solved.

[arctictraveller]

Glad you found the issue. Most problems with a lack of power at the fuse box stem from the starter relay and the attached fuseable link.