RV Electric - I am obviously a novice

For anyone keeping score, here is the latest - which indicates my prior assessment is incorrect. I used the positive wire from my alternative 12v source and attached it to the circuit board for the bed lift. I kept the original ground wire (from Forest River) attached to the circuit board - IT WORKS. Am I correct in assuming then that the ground is NOT the problem? Further testing was this: Ground wire from alternative source attached to the circuit board for the bed lift and positive wire from the original source (from Forest River) attached = meter reads 15.3, but bed will not move. I do hear an usual beep/screech/crackling noise from the circuit board during this testing.

My original guess about the ground wire "failing" was this: With original wiring (from Forest River) in place I kept the meter on the positive and negative wires while wife ran the switch. The meter drops to zero each time she activates the switch.

Any new insights??? I am on the verge of running new 12v power to the bed because its an easy fix and I am TIRED of trying to figure this out. Thanks much.