I've searched the web and here... Also the carb section where there is a sticky... Still confused.. My local shop wants to do it internally in the valve body for $450, but, I feel since I already have the parts listed below,, Why not try it?

I have swapped a v-8 carbed 5.0 in a 1991 3.1 body,, all I have left to do is install a lock up for the transmission.. I have a vacuum switch and external N.O. pressure switch found on ebay..

I found that my b wire going into the 1987 case has continuity so it is presumably a NC switch internally.. can I just wire the B and D wires to complete the ground with the vacuum switch which has both a NC and NO posts or do I still need the external NO 4th gear switch screwed into the side port of the case with just the D with to ground.. Leaving the A+ wire conected to the brakes... This car does not have Cruise, but guess that the brakes should still power the solenoid.. Or do I really just need to man up and reopen the case and change the internal switch to a NO.. Thanks

Pic found on web

 

I think you'll find the vacuum switch doesn't work all that well to control the converter lock-up. I tried one of these back in the day in my S10 but since there is not much hysteresis I found it would cycle back and forth if the throttle was held close to the switch point, which got annoying really fast. I ended up just using the toggle switch all the time, and teamed with the brake light switch breaking the hot when on the brakes, it worked great. You just have to remember to unlock it when you are going to give it heavy throttle or you come to a stop. I liked to lock it in 3rd sometimes too when cruising through 30mph streets, so I didn't utilize the internal 4th gear switch in the trans either.

 

Good to know, I never have used one before.. This one has adjustability and thought it would be needed if I used it with the external N.O. switch.. Guess I'll just wire it all up and see what happens..