Thanks everyone for your suggestions.
Updates:
1. Mike - Assigning the engine to train 0 did not work - I tried it a few times just to be sure. I also tried a TMCC reset / full reprograming.
2. ThatGuy - The front LED appeared to be unresponsive when tested with a AA battery. The rear LED lit up. I ended up breaking the front LED while trying to remove it from the clear headlight lends it was wedged into, so that one is out of the picture completely. The rear LED easily slid out of its lens.
3. Boilermaker - I actually had removed the number boards already, it's not obvious in the photo but it is just resting there. I broke the LED trying to remove it from the clear headlight lens, so that one is being replaced regardless.
Current plan, if I can't figure this out, is to just tap into the power feeds directly as Boilermaker suggests. Tap into the feeds that power the rear marker lights for the front headlight, and the feeds that power the front marker lights for the rear headlight. I have 3 mm LEDs that will fit. Wires will be all over the place, but it'll work.
I'm still also willing to swap out the complete harness if anyone has a lead on the part.
~Chris
