I am swapping to a 700R4 and have learned much from TC and those that have gone before. That said, I still have a question.

I understand that I can do 4th gear lock-up with either vacuum or 12V. Could I or should I do both 12v and vacuum lock-up?

With 12V, do I hook the wire from the trans to a cruise control brake light switch and then to a 12V ignition source?

Thanks,
Brent

Lots of folks including myself are just using the 12V lockup. Vacuum lockup control will disengage the TCC clutch when your manifold vacuum drops below a certain level. In other words when you hammer the throttle, the TCC will unlock to give you some torque multiplication. I eventually plan to put a 5 speed manual box in mine and get rid of the 700R4, but otherwise I'd put the vacuum switch in for improved performance.

Reading on in your question....the 12V source should cut off when you apply the brake. Here again, there are lots of folks running without brake switches. What the switch does is help prevent a stall (not to mention improved braking performance) during a panic stop. Otherwise the TCC can remain engaged and attempt to turn the wheels while you're stopping. I'm not sure about using the cruise control switch since I don't know exactly how it's wired, but it's a possibility. One of the more clever tricks I've heard of is to use the existing brake light circuit to trigger a relay that sends 12V to the tranny when the brake is released and opens when the brakes are applied.