Pulled wire loose or extra?

I have 78 ford van ( RV with Van cab) with 460 engine. I was changing belt on alternator and there is an extra wire, I dont know if I knocked it loose or if it was already loose. On Alternator it has the big wire and then smaller red and white wires. The red one goes into a plug-in recepticle that has two plugs. Should the white wire be hooked into this other plug? The alternator also has a stud with a nut on it that could have a wire on it but I dont think it is used as the nut is rusted to the stud and didnt look like it has been used. With white wire unhooked it seems to charge ok(by looking at voltmeter in vehicle). White wire coming out of plug has voltage. I didnt want to run vehicle too long if white wire is supposed to be hooked up. Any ideas on what the white wire does/ is it needed or extra?

I found out the white wire should go to the electric choke if present