Well, the ECM (7747) mediates lockup for that 700R4. The plugin for the lockup is a little four pin style square plug (with only three pins if I'm not mistaken) that plugs into the driver side of the transmission above the pan. The plug may be not tightly plugged in (happened to me), the brake switch may be bad, there may be a wiring problem, or possibly one of the integrated circuits or diodes in your ECM could have damaged itself causing intermittent functionality. I would say the last option is the least likely, especially if everything else is running smoothly, but it happens. You can get the plug quicker in any auto parts store if you need but cheaper online. Really the most complex part of fixing it is if it needs wire tracing to repair damage. If there's a break, it'll likely be under the car where critters and elements can get to it. You should also be able to bridge Pins A and F on your ALDL connector with a test light to gauge functionality of the TCC lockup. That external setup is generally unnecessary for a vehicle made after '80 with either an ECM or the requisite vacuum switches for the carbed guys. You should really only need that Monster or B&M thing if you're running an earlier model vehicle that's getting a lockup tranny or a manual to automatic with lockup swap, and you don't want to fool with emanating a factory setup. His connector (if he has a TH350C) looks exactly the same and should be made to work in a similar fashion.
