HI,
A heavy duty battery cable for 12volts is not the same as a 6volt cable. 6 volt cables at a minimum should be 1/0 cable or better yet 0/0 cable size. Also, a good idea is to run you ground lead from the battery to one of the starter bolts
Do as suggested and crank the engine over and check the battery cable connections at the battery and the the starter.
6volt systems tend to be temperamental about good connections and cable size.
AS stated above amperage draw is twice that of 12 volt systems, this is true of all components. That is why so many people convert to 12 volts.
Good Luck
GMCPic
Dance like no one is watching,
Sing like no one is listening,
Love like you've never been hurt.
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