Help Me See The Light ?

[srprize]

I stiil can't figure out how to hook up the back-up lights on my 70 1/2 ton stepside. On the side plate of my three speed manual where the 1st & Reverse shift fork comes out, there is what looks like a switch. It has a ball bearing at the end that rides against the shift fork shaft. the shaft has an offset cut into it that applies pressure to the ball bearing when in reverse.
the other end of the switch has a single electrical lead that attaches to it. But I dont' know how to hook it up. HELP!