No power from the battery

Hi everyone, I have a 70 Barracuda project with a 440 that ran fine until I took the battery out to try to start another car. When I put the battery back in the cuda I had reversed the cables on accident (it had been a long day..) but I realized my mistake and promptly switch them back to + on + & - on -. When I opened the door the dome light didn't come on and of course it didn't start either. There was zero power coming from the battery. I had the battery checked and it was fully charged. Today I tried it again but I had pulled the ignition lock out of the column on accident (it pulls right out) and when I put it back in the dome light came on. I didn't try to start it yet because I wanted to replace the light switch on the dash first because my tail lights have not been working so I figured it might be a bad switch. I had an extra switch that I wasn't sure was good or not but I thought I'd give it a try. So I disconnected the battery, replaced the switch, and reconnected the battery. The dome light came on again. I turned the key over just to test the lights. I flipped the switch for the headlights and the dome light goes off and no lights. Now I'm back to square one and no matter how much I fiddle with the ignition lock it won't come on again. I'm terrible with electrical obviously..is this possibly a bad ignition switch? Would that cause me to lose all power from the battery? Thanks in advance for the help. Sorry for the lengthy story.

Can you afford an automotive electrician? How is the rest of the wiring on the car? Might be worthwhile getting it to an expert if you can afford it, or ask all your friends if any of them are better at electrical.

Could be lots of potential faults ar even multiple problems.

Are you sure the battery itself is still good?

Fuses and Fuseable Links?

The Firewall Connector?

The Alternator and/or regulator may be fried.

The Ignition switch or Starter Relay, dirty Battery Cables, Bad Grounds, etc.

First I'd borrow a known good battery & set it in there & connect (1) cable only (either one) then wait till it is dark & touch the other cable to the other post & see if you have no spark which tells you nothing is on (doors shut/everything off of course) & nothing should be on at that point (nothing on = no spark). Not sure how putting the battery in with reversed polarity messed up things inside the car (other than the battery) but that'd be a start

Likely burned the fusible link. That's one reason they're used.

What he said

Okay I'll check that and see if it's the culprit. Would the dome light still come on if it were fried though? Because I did manage to get the dome light to come on when I messed with the ignition lock.

Hate beating a dead horse, poor guy. First area that I will always check is at the miserably designed connector that ties the ignition switch to the under dash harness, followed by the bulkhead connectors.

I just ordered up a replacement under dash harness for my Challenger as I have tired of dealing with this flakey ill conceived connector. Not the only reason, but the one that pushed me over the cliff,,,some 600 bucks minus current Year 1 discount of 25 percent.

The fusible link idea is another reasonable thought as posted above.

Does any other electrical function on your car,,,brake lite and dome lite are on same fuse.

We are assuming that your battery cables are securely tightened and clean at each end.