Weird, my 81 wasn't wired like that. Does the 82 run off of a different wiring diagram?
The regulator doesn't go straight to the battery, it ties into the brown wire which then goes to the fuse box, then the ignition (in some roundabout way), back to the fuse box via the red wire, through the starter solenoid, and finally to the battery. So somewhere in this plethera of wiring, there is a bad connection.
so what the diode is doing is a form of voltage rectifying (rectifiers have 4 diodes) and this stops the AC pulses from affecting the DC relay and feeding back to the alternator.