Installing standalone. What does this black plug go to? Heavy gauge black wire. It's below the brake booster next to main plug. It been awhile since I ripped everything out. 79 Rx7.

 

Just looked at my 1979 GS. I don't have that plug. I do not have AC just for reference.

 

Looks like the hot start assist connector. SA's Should have 2 wires, a solid black and a green / red stripe. The wires for an FB may be different. I know the connection at the assist motor is different btw SA's and FB's