Hi,

I had the same problem with my 122. The "switch" is realy a ground contact on the upper part of the transmission behind the shifter. You can access it from below. Check to see that when the transmission is shifted into reverse that a ground connection is made. I hooked my test light up to the positive side of the battery then shifted the transmission into and out of reverse. If the light goes on and off, then the problem is most likely in the relay on the righ-hand fender under the hood. If there is no ground connection then you have to take the aluminum cover off and see what's going on. In my case, the little spring that makes the ground connection was bent and not working (always grounded). I straightened it out, and put some tubing on the attaching screw so contact could only be made by the transmission selector rod. So far works fine.

Check the relay by jumping it to the ground on the battery (follow the lead from the transmission up to the relay). If the lights go on, and the relay clicks, then it's OK. If faulty, replace. All of these instructions preclude a working tail light assembly (bulbs are not blown, wiring is unmollested etc). Check these all out first. It took me a day to sort out, but wasn't hard in the end (with many thanks to the list).

Cheers,
Craig