I would like to add my two cents worth if its not too late. Firstly ,never over ride any safety (PMT) feature on any system. Secondly this problem sounds like a function of load (current demand) not scr switching. Components like battery,cables even power fuses should be checked for VOLTAGE drops under as much current load as you can apply before drop out. You must track voltage drops@battery and across everything in the power circuit down stream ,resistance measurements under no load conditions are inconclusive.Start at the battery and move down stream UNDER CURRENT LOAD until you measure a suspicious drop across a component or connection. (What are the coildriver signals @ the contactor coils doing before they drop out?)