On the dash and in the engine harness there are many items that need either a common power or ground. I like to use one common wire and splice all the other leads onto that wire. Strip the primary wire by using an Exacto-style blade to circumferentially cut the wire in two places were you want to strip it. Longitudinally cut the insulation on the wire between the two circumferentially cuts. Strip the insulation off the wire. Then strip the insulation off the end of the wire that you want to add in.