700R4 Torque Converter Lockup Kit 500412 Pressure Switch

A 700R4 will shift into fourth on hydraulics alone, but the torque converter clutch will never apply unless something feeds 12 volts to the case connector. That is the problem in almost every carbureted swap, street rod, and older truck running a 700R4 (TH700-R4) or 200-4R behind a non-computer engine: the trans goes into overdrive, the converter stays unlocked, and you get 200 to 400 rpm of permanent slip on the highway. That slip is heat, and heat is what kills a 700R4.

This kit is the wiring and switching side of that fix. It uses a hydraulic pressure switch that threads into a 3/8 NPT fourth-gear pressure port on the transmission case, so the converter clutch is only allowed to apply once the trans is actually in fourth and fourth-gear apply pressure is present. No vacuum switch guessing, no manual toggle you have to remember to flip off before you come to a stop. The kit includes the pressure switch, the harness to reach the case connector, and an in-line fuse.

Read this before ordering: your case must have a 3/8 NPT fourth-gear pressure port. Many 700R4 and 200-4R cases have the boss cast in but not drilled and tapped, and it has to be done with the pan off and the trans out or well supported so no chips fall into the valve body. Check your case first. Most builders also add a brake-pedal switch in the ground leg so the clutch releases the instant you touch the brake. Manufacturer part number 500412, fits GM 700R4 (TH700-R4) and 200-4R (TH200-4R) four-speed automatics.