That wire wound resistor is something like a 30 watt dissipator, or more. And, in normal operation dissipates 15 W max.
Have you measured the field coil resistance? S/B about 5 ohms (550) 0r 6.8 ohms if 750. If that white wire has lower resistance than that, it would explain the overheat, (or if the white branch is shorted to ground).
I think you have have wiring issues.
Cheers,