Cigarette lighter fuse?

Am thinking that I could use that hot lead for the under hood light as power for the USB. Am thinking that lead should be on a fuse somewhere.

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Before I connect anything to the lead I will test it with my multimeter. Has anyone ever used a battery cutoff switch? Am thinking it might be a nice thing to have for long term storage and maybe theft prevention. I know its pretty easy to get under the hood in a TJ but might serve as a little deterrent.
 
I need to put a tow vehicle to Jeep wiring harness so I can flat tow this Jeep. Am thinking about using this one. Has anyone used it or can they recommend something better. I like this because its plug and play.

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