First, do as LTG says, because he is LTG.
Then, check what kinds of switches you put in the cab. Does Elvis use those crazy crossed switches from Stern? Are they the same type on both sides?
I’d also pull out the linkage to make sure it isn’t binding, Has no extra play, and has that spacer between the bolt and the plastic.
After that, I’d be swapping parts left to right. The coil, the switches, right down to the transistors. At some point of swapping, you will find the defect.