The switch is on the right side of the trans, secured with a big center nut on it's input/gear position shaft and a smaller (12 mm?) screw, oval hole. Removing the exhaust pipes isn't necessary but will provide far better access to the switch. Sometimes the switches are a bit tricky to slide off the corroded/dirty shaft end - careful cleaning is the solution.

Adjustment is possible after loosening the screw but you should note that the switches don't normally go out of position. If the switch doesn't appear to have been replaced or otherwise fiddled with, just replace it. From what other posters have written, I'd roughly calculate with a life span of 100k miles or less. A simple special tool or some skills with an ohmmeter is required to adjust the switch position properly. With the tool, I think it's about lining up the cast mark in the swith housing with the input shaft in a certain gear position. Not sure, have never used it myself.

Before replacing, make sure that the electric connectors (grey plastic block on the left side of the trans) are ok, clean and not oxidized. Connectors will be stuck and the plastic brittle - don't break anything.

/Martin
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'65 121, '73 165