700R4 200-4R Torque Converter Lockup Wiring Kit

This is the lock-up control kit (P/N 376600) you need when you drop an overdrive GM 700R4 or 200-4R behind a carbureted or non-computer engine. Those transmissions have a lock-up torque converter clutch, but without a factory computer telling it when to apply, the clutch never engages. That leaves the converter slipping in overdrive, which means more heat, worse highway mpg, and a converter and fluid that run hotter than they should. This kit builds the control circuit that makes the lock-up work.

It runs off engine vacuum. A vacuum switch references manifold vacuum and engages the converter clutch when you are cruising at light throttle, then drops it out under load or when you get on the pedal, the same behavior the factory logic gave you. A manual override lets you force lock-up on or off when you want it. The kit includes the vacuum switch, the wiring, and the terminals to splice into the transmission's TCC solenoid lead.

Installation is a pan-off job: you tap into the lock-up solenoid feed inside the transmission, route the harness out through the case connector, mount the vacuum switch to a manifold vacuum port, and tie in a brake release so the converter unlocks when you hit the brakes. It fits the TH700R4 and the 200-4R (2004R), and also works for a 4L60 that is not being run by an electronic controller.

One field note from techs who have installed this: bench-test the vacuum switch before you cut into your harness. It is a simple check with a hand vacuum pump, and the printed instructions are terse, so watch a 700R4 lock-up wiring walkthrough first and confirm the switch holds vacuum. Do that and it is a straightforward afternoon job.