Power failure of Navio2 or power module

Last November I purchased a Navio2 with power module and set it up with the following hardware on a rover:
-dimension engineering 2x50A motor controller
-FS-IA6 Receiver
-I2C Telemetry

Starting from top left PINs connected to Navio2:
PPM output of FSIA6, FSIA6 +, FSiA6 -,
Signal1 to motor controller S1, + to motor controller +5vdc, gnd connected motor controller gnd, signal 2 to motor controller signal 2, + to motor controller +5vdc, gnd connected to motor controller gnd.

(Sorry I have a diagram and pictures but it will not let me load them)

I was able to operate my rover in manual mode with RC transmitter and in auto mode via Mission Planner with no problems at all. Very simple setup.

This winter I spent time modifying the rover chassis. All electronics was disassembled and stored indoors.

Finally this spring I had the chassis ready for another test and instant power failure. This failure killed Navio2, Motor Controller, and power module.

The Pi survived, and I can also power the Navio2 via PI but I have bad health warnings on GPS/ AHRS, and have not tested any of the signal outputs yet. Power input via 6-pin connector is dead(shorting, high current heating). But I can power it via the rails where the motor was connected

Any ideas where to look? Any component numbers for replacing power input for power connector. More details on the ‘triple redundant’ power of navio2 ?

The motor controller was very expensive for me ($180USD) so I need to get to the bottom of this before I try again.