Bad ground? Could you bypass the mast wire with a jumper and see if that's your problem? Also you can do a continuity check for the mast wire.
Good luck

Last edited by JiMerit Boltr#43; 04/26/2014 5:35 AM.
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1946 1/2-Ton Chevy
1953 Chevy 3/4-ton Factory Stakebed