Ben;

From your description of symptoms, I also believe the VR might be the source of the problems, because in the first place, if gen runs like a motor, that's a very good sign...but if AMP light stays ON when IGN is OFF, that points right to the VR cut-out relay. [Cut-out relay contact is not dropping out when gen is not putting out power, as it should...under normal operation this disconnects battery from gen output from battery when engine is not running, and prevents gen windings from discharging bat...this would explain AMP light being ON when IGN was OFF]

Things to do and check:

1. State of all connections at gen, VR, starter, bat, and also connections around and state of Fuse1...if connections are poor/questionable, just about all other work or troubleshooting is almost worthless.

2. State of field brushes within gen. If these are worn down and not tall anymore, they will have less spring force holding them to the commutator, and wont be able to carry much current. As a strictly temporary road fix, turn worn brushes 90 degrees and reinstall them. No guaratees on how long this will last, but unless it's a x-country trip (no pun intented), it will many times at least get you home.

3. Check VR cut-out relay (that's the one with the heavy gauge coil wiring) for a welded cut-out contact (that's the contact which connects to the B+ terminal of VR). Take cover off VR (pick away paint seal, unscrew single philips holding screw, without shorting metal cover to internals, lift off cover). Cut-out contact should be open when IGN is OFF...even at idle...it will only close contact at elevated RPMs, when gen is actually putting out power...then, as RPMs drop again, it should open contact - and STAY open when IGN/engine is OFF!

4. Don't run aux lighting (100W = 8.5A) and a high-power audio system (400W = 34A) at the same time. Contrary to other post, unless audio amp has a problem which would likely blow its fuse, it does NOT pull full power when output/volume is low. Nonetheless, just add up those two auxillary loads, and you're already way above the rated output of that poor genny...and that's before you run the ignition, headlights, and occasionally directionals and brakelights...I realize it wont help you right now, to get you where you're going, but if you want to do that, it's 60A alt upgrade time!!!

That's all I can think of immediately, let us know how you make out.

Good Luck