As for wiring diagrams, the TH400 doesn't have much electrical input. The downshift solenoid is about all I can think of. I doubt you have a variable pitch stator and I don't believe the TH400 ever had any TCC option. According to the GM shop manual, here is the list of all external controls (electrical and otherwise):
EXTERNAL CONTROLS
The external control connections to the transmission are:
1.Manual linkage to select the desired operating range.
2.Engine vacuum to operate the vacuum modulator unit
3.An electrical signal to operate an electric detent solenoid.
4.A stator solenoid to "switch the pitch" or stator angle. This device is used only with transmissions having a variable pitch stator.
Anyway, here are the diagrams for the 4WD indicator light (actually the switch is mounted on the transfer case) and the downshift solenoid: