Need help with the final frontier...

I think I have my electrical pretty well sorted. It's my 1974 Dodge Power Wagon. I'm putting in a total aftermarket 20 circuit hot rod kit for the wiring. Pretty well labeled plenty of wire but just a couple things that are not addressed...
Mainly the three prong transmission wires relating to the starter solenoid and the backup lights.
To where I have it understood in my head is the red wire is the battery and battery powered for my fuse box with a fuse link. The small black wire indicated in the picture here goes down to the starter. The yellow wire coming in is the one that when I turn it to start gets juice and the brown wire to the bottom right is the one coming from the center of the three transmission wires that's actually a ground that allows that start electricity to go through when it's in park or neutral? And the two wires on the outside of the transmission prong one going in with constant juice when the key is in the run position and the other coming out with juice to the backup lights which is connected when in reverse?....
This seems to be my last hurdle for getting all this 100% figured out...
Thank you for everyone's experience and knowledge...

Yes the 3 prong neutral safety switch on an automatic sees continuity on the outer two prongs when in reverse for reverse lights.
It is grounded in Park and neutral for start.

66 Valiant wagon said:

Yes the 3 prong neutral safety switch on an automatic sees continuity on the outer two prongs when in reverse for reverse lights.
It is grounded in Park and neutral for start.

Click to expand...

Thank you for that and I'm assuming that ground is the ground for the starter relay that makes it work?..

Yep, ground for the starter relay.

66 Valiant wagon said:

Yep, ground for the starter relay.

Click to expand...

Thank you very much for taking the time to clear that up. Again not addressed in an aftermarket wiring harness. I basically just get a Chevy style start wire that runs the length of everything...
Parts of the wires are straightforward but then you get brand and applications specific and these are just the last few I have to coordinate for that.
Again greatly appreciated...

It's the center pin on the NSS that is the Park/Neutral ground for the starter relay. The outer pins are the ones for the backup lights.