I've never tried one on 6V, so I can't be sure, but it's highly unlikely the module would trigger properly. The whole system is designed to run at maximum charging system voltage, 14V+, and when we tried to use a HEI setup on a race car with nothing but battery voltage, no alternator, the results were pretty disappointing. Just adding a low-amperage alternator turning at about 1/2 speed with a big pulley made a noticeable difference in the performance of the ignition system.

The module has a built-in low voltage safety circuit that maximizes current flow anytime voltage drops below normal, but it's not likely a 6V system would be able to reliably trigger the module even with that circuit operating. I've got a HEI system set up in a distributor tester at school, so it would be a simple thing to just swap batteries for a 6 volt and see how well it works, if at all.
Jerry

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