I drilled down through the plastic truck frame #80 .012 to insert a removable piece of .010 brass wire held in by friction, contacting the frame halves.
That gave me the frame electrical leads I needed to set up the dropping resistors and the LED's. And I can simply pull those wires out with tweezers if I have to get the mechanism apart again.
You can't solder to those frame halves, and there's precious little material to put a screw in either.