I think I see what could be a small triac, does that run the light that's not on or is the light powered from the radio board? Just curious what common chip could affect the motors and the light as well...one of the voltage regulators?
It sounds like there are two different failures here. In looking at the wiring of the crane car, if all the lights and all the motors are dead, that says the motor driver board isn't doing anything. However, if only two motors are dead, I'd be more inclined to suspect the drivers since the board is somewhat alive.
The couplers and outriggers are driven by a separate board that appears to receive serial data to directly control those items. Only three wires go down from the crane, power, ground, and a 3rd wire that I have to believe is serial data.
If you don't have it, the wiring/parts diagram for the crane car is actually excellent for seeing what is connected where.
Here's the link to the documentation I mentioned, well worth the download.
Thank you. Very helpful.
Jon (SantaFefan) - did you find anything more about this cluster of motor driver(?) problems?
I'm sending my board in with the demo sensor car this week.
Any updates on the motor driver(?) problems?
Success!!!!
My replacement "CRANC" driver board from Boxcar Bill (MTTP) arrived on Saturday.
Yesterday, I held my breath and VERY carefully removed the 6 screws holding down the shell and then clipped the antenna lead, all while keeping the car upright to avoid tangled strings.
The shell came off surprisingly easily and the the hardest part of the job turned out to be removing the 6 connectors from the old board without damaging the wires.
Fortunately, I took photos of the connectors (several of which look identical) in place before removing them so, plugging them into the new board was easy.
All that remained was to re-address the new board and everything now works perfectly.
After all the warnings about tangled string and difficult internal conditions, I was dreading this repair but, it only took 30 minutes from start to finish and cost a lot less than sending the crane car away for repair.
I want to thank GRJ, Boxcar Bill and MartyE for their help on this.
My visual inspection of the old board doesn't show any problem so if anyone can tell me how to figure out which component(s) failed, I'd appreciate some advice.
It's good to hear success stories. 
