Well....I'm tapping out.
Need GRJ or one of the other TMCC guru's to chime in here.
Bob
Well, Bob, I took my Sperry speeder apart (again) and figured out the cab light. It turns out that the small circuit board cemented in the roof of the speeder cab has two circuits, one for the roof beacon and one for the interior cab light. The cab light circuit uses a chip led (with a clear plastic diffuser that makes it look like an incandescent) that takes "hot" A/C directly from the collectors and ultimately returns it to the same ground as the beacon, front and rear lights. I'm guessing there's a diode and resistor on the side of the circuit board I can't see.
For the rail bonder, then, I'm going to use the circuitry from an Evan Designs universal kit, solder its output leads to the wires feeding the nicely-mounted rail bonder cab "bulb" LED with correct polarity and power it directly from the track. I'll coat the LED with white acrylic to keep the crew from getting a suntan