Steve,

Nice diagnostics. That #61 terminal should be about what you see and not zero ohms to ground, normally, I think. I've never measured with a multimeter, so in a few minutes I'll check a spare on the shelf and come back to this thread with any change in thinking. What you report seems to me plenty "ground" to effect the lamp test.

Edit: I checked two alternators. 68 and 70 ohms respectively, regardless of probe polarity. Both have Bosch regulators, which have the 68 ohm resistor.

I notice you proved the wiring to the alternator exciter OK by seeing the lamps full brightness with key on and the wire taken directly to ground. How do the lamps look when you put the wire back on the D+ (#61) terminal?

My next step would be to pull the brush pack and check out the brushes and slip rings, if I felt confident the blue wire terminals were solid and the D+ wire proved OK as you did. I'd get a good look with flashlight and mirror at the slip rings. These alternators are coming of the age where slip rings can be worn beyond service, so if the brushes seem to last fewer miles than they did, consider the surface inside. If you take the belts loose, feel for play in the bearing while you're there.
--
Art Benstein near Baltimore

I find it ironic that the colors red, white, and blue stand for freedom, until they're flashing behind you.