[BlouDon]

Well, the 700R4 install has now been running quite a bit ... without 12V connected for Convertor lockup.

Did so today:
12v on pin A
GND on pin D

That's it. No in-line vacuum switch. So what happens?

It pulls away in 1st and very quickly locks, in 1st. Thereafter it remains locked for upshifts & downshifts into all gears. Shifts are not harsh at all, but positive.

Downshifts are OK, but engine speed does seem to dip a bit low when coming to standstill. Not a train smash though.

I concluded that either a foot controlled TC engage/disengage switch or a vacuum switch is called for. Best yet would be a speed based engagement. Should not be too difficult to do with an Arduino Uno.