I have a third gen 4runner and was wondering which is the power wire for the power outlet? The wires are purple, black, and white. Thanks

 

a test light will tell you every time!! hook the clip to a ground and touch the light end to the wires( one at a time) when you find the hot one the light comes on!

 

there are 3 wires going to your power outlet? If it was just black and white then white will be hot and black will be ground, in your case purple may be hot but I don't recall seeing a 3 wire power outlet ever.

Unless you somehow have an AC power outlet in your truck...in that case it all depends on who put it in (not sure if toyota ever used factory inverters).

Either way a multimeter is your best friend