12V Negative Ground Wiring Diagram

For a system with the coil dead in the off position, the black wire that normally goes to the coil from the junction box will instead go to the ignition switch, or the red wire that normally runs from the coil to the ignition switch can be run to the junction box where the black wire was. The wire that is normally in the armored cable that goes to the distributor form the ignition switch will instead go to the coil. If it is a negative ground system that wire will go to the positive side of the coil. If it is a positive ground system that wire will go to the negative side of the coil. The other side of the coil will go to the distributor.

This works well with an aftermarket ignition switch. If you have the original pop-out ignition switch you will have to cut the armored cable near the ignition switch and do some wire splicing. Cut the armored cable with a Dremel cut off wheel being careful not to cut the wire inside. Cut it in two places and take a section of the armored cable out to access the wires for splicing.
 
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If you have a generator, you also need to change it polarity. Someone also posted about just swapping the coil wire without changing the ground, that will only work to a point. The coil needs to have the current flowing the correct direction for best power.
 
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