I would enter test mode and check the switches there. Hopefully it doesn't say "every switch open".

I didn't think that BTTF had switched solenoids but what you're describing is a switched solenoid (with respect to the bumpers and slingshots). IPDB lists this game as DE-V3. It's the first one so it may not use CPU controlled solenoids for the bumpers and slingshots.

The other thing you can test with respect to the relay on the PPB is the coil tests. Just let it run and make sure everything that it says it's firing (coil or flasher) actually fires.