I don't think it matters as they both are field wires. But the shorter one goes to the bolt closest to the pivot bolt, and the other wire goes to the farther one.
............Check the wires with the key on, engine off.......whichever wire has power goes to the field terminal closest to the pivot point...........kim........
As 67Dart273 says, it doesn't matter which way you connect. That is because it is an AC generator, hence the term "alternator" which replaced the older DC generators. The diodes convert the output to DC and "rectify" whichever direction you connect the field. However, to match the factory, use the wiring suggested above.