I have been using the search function for starter wiring.Everyone says there are three large red wires and a purple to the starter.I have these wires but my red wires go to a fusible link with orange wires coming out the link.Two of these orange wires are factory crimped together and the other is a single crimp.This harness reaches the solenoid and hooks up as should.BUT I have another large red wire with a fusible link and a piece of orange wire with the end cut off,this wire will also reach the solenoid.It is in the same harness but has a small plastic loom on it like it may go somewhere else.I have located the alternator wires so I am sure it doesn't go there.
I am trying to put wires to their respective locations,at least the one I need.I can start the engine with the key switch now so I have made progress.This car was used as a parts car so I am not sure what should be working or not.I just didn't want to smoke test anything by having this wire hooked to the starter.
By the way I am working on an 88 vert that has been converted to a carb,HEI and a manual tranny.

 

As you say, one is for the alternator. Then one is for the lights, one is for the ign key, one could be for the A/C (blower), one could have been for the EFI (ECM), and one could have been for a coolant fan. I'm speaking in general terms here as I don't have the diagrams for your car before me. If you want you can try a temporary hookup, passing the current through one or both filaments of a spare headbulb. If there's a short the bulb will light up fully instead of anything smoking.