I don't think that brake line pressure is the problem.

It's a wiring problem, but without actually working on the car themselves it's tough for people to tell you where the problem iles.

With it being wrecked there are so many places that there could be wiring damage.


It's just like any other old Mopar, it there is power at the starter (large hot lead) you should be able to feed power to the starter solenoid connection on the starter to make it crank over.
Whether it would actually start with the key in the on position is a whole other story.