Hey Brad, if you're trying to determine how much current the lighting draws why don't you just get a large power invertor and hook up an ammeter/multimeter in series with one of the leads going to the cigarette lighter. You can measure the total DC current drawn (this includes the power loss in the invertor). Use this to calculate approx how much power is required:

Power (Watts) = Voltage (14V) x Current (Amperes)

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