When I wired up an electric outlet I went from the starter wire connection to an automotive inline fuse, to the outlet. The 2nd wire of the outlet needs to go to the chassis or frame.
I used a 15 amp fuse, as the outlet can become the most easily accessable place to hook up a battery charger.
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In daily life we are more often liked for our defects than for our qualities.
All the best,
Diceus