well i cant seem to get any lockup in my 700r4 truck trans with a tpi motor in my fullsize truck so ive been told to do this.....I personally like the 1 wire hook up, 4th gear only lock up. If you agree, I can describe how to wire it up. Easy to do and the hydralic circuit in the valve body will force a lock up upon shifting into 4th gear.......Here is what you want to do:
First confirm that terminal A on the connector goes hot with the ignition on.
Then drop the pan and filter.
Look closely at the inside harness. Terminal A should go to the red wire on the lock up solenoid. Be sure it does. Then cut the ground wire off the solenoid, leaving plenty of wire on it to solder a lead to.
Find the 4th gear lock up pressure switch. It is a single wire , normally open switch. Remove it and put 80 psi to the inlet and read it with a meter to be sure it is opening and closing properly. If it is, great, if not toss it and buy a new one. Wire the single terminal of the switch to the ground side of the solenoid. Cut and remove all other wires. If the car has a 4-3 (2 prong) pressure switch, simply leave it installed where it is ans it will serve as a plug for the port it is in.
At some point be sure to check the pos and negative of the solenoid for the proper ohms. At room temp 22 ohms is typical. 15-50 is ok, but you will hover around 22 ohms.
When hooked up properly, 12 volts are always on the positive side of the solenoid when ignition is on. Upon shifting to 4th, the pressure closes the switch and sends the ground triger to the ground side of the solenoid. Viola! 4th lock up only.
If this is done as described, and it still won't lock, you have internal mechanical lock up issues.
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has anyone done this befor if so how do you like it and is there anythin bad that could happen to the trans by doin this? also can anyone help me with were these parts are in the trans ...pics/diagram or anythin...i have never been in a trans befor so this is all new to me... thanks again

 

does anyone know about this?

 

It works just fine, but it assumes that the 4th gear switch is N.O., which it isn't for the vast majority of thirdgens. Try it on one of those and you'll end up with a TCC that stays locked in 2nd and 3rd but unlocks in 4th.

 

how do i tell if i have a N.O. or N.C. 4th gear switch in my truck trans? if i find out i do have a N.C. one can i just buy a N.O. switch and then do this setup? anyone know the part# on the switch i need?

 

8627332 or 8642473