The pac-brake solenoid gets its power from different sources for the two different modes. In warmup it originates at CB77 via the trans neutral relay K26 and the brake/warmup switch Then on to the solenoid and ground.
In brake/retard mode the solenoid power originates at the ECU And is enabled by a relay controlled by the trans control unit.
Since the CB77 power is available all the way to the warmup/brake switch whenever the trans is in neutral, I agree the solenoid or it’s wiring to the switch may have a short. MCB77 is supposed to be a 15A, is it working right? You can plug in a standard automotive 15A fuse or swap it with a different 15A breaker…
The ECU power output is probably current limited, so it is not allowed enough current to pop any other circuit breaker, but if the solenoid is pulling so much current the solenoid may not be performing any work when the brake is commanded on either… a high current draw thru that circuit may also set a code in the ECU…
