I would have said fusible link - but you checked that.
Does it crank if you jump the starter relay on the inner fender? Check all the connections there while you are at it.
Dave is right on checking the ammeter wire to see if there is any juice getting through the bulkhead connector. If not - there is a loose or cooked wire at the bulkhead connector.
I do like the color combo

Yes it cranks when I jump relay on fender, found power thru bulkhead connector , spotted some corrosion in connector but ran out of time and Advil.

Welcome to Mopar! I have a color wiring diagram for a 71 Challenger if you need it.

You can have power going to the gauge.... just need to have power coming back out of it. Identical problem I had, and a fried ammeter was the culprit. Since it was running then died, it makes me think that this is the problem as well since you can jump the solenoid under the hood. But could be one of many small issues all compounding into one.

Easy to hook up a new ignition switch too. Just plug it in to the connector and ground it, then try to start the car.

Cheers
Dave

Bingo...pulled apart the bulkhead connectors and cleaned etc but nothing. Then pulled the aftermarket radio to get at the ammeter, put a jumper wire and bingo. Same thing happened with my old Toyota 2000GT. Took me forever to find it that time. The bigger issue is my "old man skin". It gets depressing when every time you bump or scrape against something you are bleeding. I used to do this stuff for a living and now I need a supply of bandaids and Advil.

Look at it this way,after you die,a DNA trace test on that car now will verify it's past ownership history.

Charley, you're way too delicate for a car like this. Ship it one of us manly types who can really handle it.

;-p

Nice to see that you found the defect. Now on with the (burnout) show.

BTW, why is the engine painted blue? Is it the original motor or has someone been in there long ago?

No idea on the engine paint but probably that way since 88 at least. Runs good. Where are engine #'s ?