How to change my Overdrive Solenoid

Depends, is the car an automatic or manual?

I've never seen a solenoid fail except for one that was leaking. Make sure you check all the wiring first, that's far more common to break.

I'm assuming this is a manual transmission with the Laycock OD unit. Check the OD switch and wiring running down the shifter.

Disconect the wires and unscrew it from the overdrive case. Although the elctronics rarely fail, if you have never changed the transmission fluid it could be sticking.

There is good info about this proceedure and also replacement parts (and a nifty over-ride plate) at IPD. Link =