UPDATE: I figured I'd post and update on my manual TCC lockup results.
I discovered that the later model 700R4's come with a built-in 4th gear switch, as mine did. It sends a ground signal out thru the main 4 wire connector, which I'll explain shortly.
You literally can simply send 12v (and ground) to the TCC lockup (pins A & D)... and everything just works from there! A switch actually isn't even needed if you were to wire from switched ignition power. [see figure 1]
Typically, wiring from pins B and D are fed to the ECM (which I removed from this figure).
I also discovered it will NOT lock up in 1st or 2nd gear in any way whatsoever, despite manually activating the circuit. Power actually opens the hydraulic circuit that allows lockup when certain conditions are met. Mine however will lockup in 3rd and 4th, if you ground the TCC lockup (pin D).
Another nice surprise to learn is that it will also disengage hydraulically when you apply more throttle, even without the ECM. NO vacuum switch is needed either! For me... manual lockup in 3rd was too "jerky" with shifting (and unneeded), so I decided to use the 4th gear switch and use it in 4th gear overdrive only.
The trick is to ground the TCC (-) wire to the 4th gear (-) output.. which goes to ground when you hit 4th gear. [see figure 2] Then (again depending on throttle pressure)... TCC lockup will automatically engage! You literally twist the 2 wires together (pins B&D), and apply 12v to pin A.
The circuit above suggests using the brake switch to disengage power while braking. This isn't actually absolutely necessary, but it will give you less jerking and a smoother ride while braking. I haven't done this yet, since I mostly use lockup primarily on the highway and haven't had any issues. I will probably add the brake switch power interrupt later at some time.
I opted to NOT use my manual latching circuit (which would have worked fine).. since the lockup works completely automatically with the 4th gear switch.. just set it and forget it! I did install a lighted toggle switch for the option to engage/disengage 12v to the lockup circuit. It lights up in 4th gear when lockup is engaged. Nice!
Mine goes into 4th (and lockup) about 35-40 mph with light/normal throttle. During harder acceleration, there is no lockup (even though manually engaged) until you ease off throttle and reach normal cruising.
With a moderate hot-rod cam I found mine can be a little "jumpy" at low rpms in 4th... so I typically disengage around town, and use lockup primarily on the highway. But with steady maintained throttle pressure at slow speeds (other than a short) stretch it's fine. Otherwise in slower local traffic it's best to let the torque converter do it's work.
As an added non-related bonus... I decided to use the 4th gear switch to also send a signal to an A/C bypass relay to the electric fan... which is not needed at cruising speeds. When I hit 4th... the e-fan disengages automatically. Nice!
I don't know what year they started including the 4th gear switch in the 700R4's.. but it sure was a blessing to find it in mine! No parts or mod's needed.. it's all already there!