Mark i have had the same problem with my engines 03 42' open with C12's . i disconnected the original battery cables , taped them up and tie wrap them to the side . Then i ran two new 3/0 battery cables , one for each engine, right from the starting battery's to the starters . it solved my problem , now i can start the engines WITHOUT paralleling to the house battery's .
Mark also its not the engine starters having a problem , its high resistance connections ether in the cables or in the battery switches . To prove the point get a length of cable 3/0 with a battery post connection on one end and a ring terminal large enough to connect to the starter on the other end and connect the easiest engine first (probably the starboard one) . Do this first before you get Cummins involved , lot less expense .
Mark also its not the engine starters having a problem , its high resistance connections ether in the cables or in the battery switches . To prove the point get a length of cable 3/0 with a battery post connection on one end and a ring terminal large enough to connect to the starter on the other end and connect the easiest engine first (probably the starboard one) . Do this first before you get Cummins involved , lot less expense .
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