Use the harness you have. Clean it up. Cut the green/white stripe and the tan /black stripe about three inches long strip the ends and solder them together insulate with heat shrink. Cover it with split loom to where it goes into the car. Run the purple wire back into the car as it was and connect to the brake light switch. Take a wire from the other side of the 2nd brake light switch connectors and;
1. Run it to a toggle switch then to a switched +12 volt source and control it your self.
2, Run it to a vacuum switch and from there to a switched +12 volt source and make it automatic.
When controlling it manually keep in mind that the torque converter should not be locked up when the engine is under heavy load.
Say you are in third and climbing a hill it needs to come out of lockup, it will load the engine too much and make it over heat. That's what the vacuum switch does, as the engine load increases vacuum will go down shutting the lock up off. If you control it manually you will have to turn it off as you climb hills and the like.
If something goes wrong and the lock up is on all the time putting the car in gear at idle will kill the engine rendering it undriveable.
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