Aside from the HEI distributor, what else could possibly be fed from this circuit (from the factory)?...

 

I think that comes directly from the ignition switch. And nothing else is on that circuit.

 

The pink/black is fed from the same ign sw terminal, in some if not most or all cars anyway, but has its own fuse.

 

The pink Ignition line is shown running from the igniton switch to c100, where it goes to the distributor. It also looks like it splices on the interior side of C100 where runs to the Turn B/U fuse, the Ecm Ign fuse, and the Gages fuse.

 

'Reason I'm asking is because there is a short pink wire of the same gauge that is spliced into the pink wire for the HEI. It has a blue connector on it, and plugged into it was a black wire (makes no sense. Since when would a black wire be used for 12V+ in an automotive application?).
I have no idea what it would have been connected to. It was years ago that I pulled the old engine out. I definitely don't need it to make the car run; I just find it really curious. My plan now is to use it to power the fan relay. This car never had an electric fan, and I'm installing one from a '84 L-69 car, with a wiring kit from Painless...

 

Not factory. I'd eliminate it if it was mine.