Originally Posted by geotherm
when using the tailight as 'turn on', should I tap into wire at plug right before bulb? Also, do I need to have voltmeter out to make sure which wire is positive? Or, is one color always the 'hot'?
Tap into it somewhere you can reach and easily work on, should you have to. Tapping into a tail light wire near a socket won't make a measurable difference in volts/current going to the relay, so why force yourself to work in the tiny space with very little wire slack and no chances to correct an error?