Ralph,
If you power your lights, and they have no way to get back to ground to complete the circuit, they won't work. When you put your test light on the frame (grounded) and touched the bed (hot), you completed the circuit and the little tester lit up.
Current flows from the battery through the wires to the lamps. Then through the filaments, which glow, and then back to ground...if looks like the bed isn't connected well enough to the frame to complete this path to ground.
If you do as Brain and others have suggested, you will probably solve your problem.
I think this is how it works.
Stuart
