1974 Plymouth Duster no power through bulkhead.

superchargedblackbird@gma said
In the second picture, the wire that is circled in blue is the ground wire that had been ran from the tach that is now completely unwired. The plug circled in purple was never plugged to anything.

This doesn't make sense to me. What brand and model tach is on the car?
I'd disconnect and tape the ground for now.
The other IDK I can't even see it.

superchargedblackbird@gma said
In the fourth picture of the starter relay, the neutral safety wire that is cut is wired into the B&M shifter's neutral safety switch, and was also working wired like this previously.

Should be OK then.

superchargedblackbird@gma said
In the sixth picture, the plug and gray wire circled in green were also not plugged into anything previously.

The connector with the double is probably for the choke assist. Follow the J2 branches on the diagram and then look at the CE connector charts

The connector in the last photo looks to me like the ones used on the brake warning switch.

The terminal blocks on the fender look really corroded. I wouldn't use them. Replace or toss and/or come up with some new junctions. What's best depends on what you will be doing with the car.

This looks like a circuit breaker