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According to the fitting instructions on the universal dual battery system i just purchased, if the alternator output is below 14 volts it may cause the controller to chatter...there is a remedy though, that being to connect the red charge cable to the main power out on the alternator (wish I knew what/where this is). Hopefully I can avoid this if the output is above 14v:???:

Output should be about 14.4v at the alternator output, unless you are pulling more than the alternator was designed for. Like driving too many driving lights.

Yes connecting the cable directly to the alternator output will give you makimum voltage.