The Nissan Path

Im planning on setting up a trailer hitch on my 89 pathfinder(2 door, se, v6)
ive been looking into it. online i have found wiring harnesses for pretty cheap, however when i called for quote from a trailer install plaxe they said you need to install a tail light modulator, becuse my model doesnt run enough juice to power the second tail light set. im not really sure what a tail light modulator does.
Has anyone self installed a hitch and wiring harness ancan help me out? do i need the modular? what is a modulator? and do the kits for sale online come with one or not.

thank you.
Alevc

what kind of trailer? do you need power just for the lights at the back of it?

if yes, then the power coming to your trucks rear lights is enough.