mudman2

Yes, the control module get fitted on Tuesday. I think part of the PST2 action must be to activate the brake control logic.

wingless

The 4-pin brake controller connector has three inputs and one output. The red wire is +12VDC, the brown is ground and the black/red is the stop light. These three inputs may be tested with a meter.

If they are all good, then the blue brake wire output is routed to the 7-pin trailer connector, bypassing the electronic lamp control module.

Yes, it may be that the PST2 is required to have the black/red stop signal operate properly, but that may be tested using a meter.