<!-- from fixya rte -->HOW TO HOOK UP TRAILER LIGHT HARNESS - 2006 Ford Escape XLT

the secret here is to buy a trailer harness for the vehicle ( available from most tow bar supply and fitting shops )
it is a set that just plugs into the existing harness at the rear light assembly ( piggy back arrangement)
from there you wire the male and female plugs as per the color code that is on the paper that comes with the units
saves cutting into the car harness and causing real electrical problems

Hook up the trailer to the vehicle. Under the rear bumper you will find a thick wire harness that runs from left to right or vica versa. Choose a location to strip open the harness to gain access to the different color wires. Open the trailer coupling. remove all wires and split them apart. Now start with say the right indicator light on the vehicle. Earth should be established via the grounding method of the trailer hook steel on steel of the vehicle. Connect any wire of the trailer to the now flashing right indicator light. Go through them all till the right indicator bulb flashes on the trailer. A good approach to determine which wire is active, is to make a test light from an old bulb connector some have already two wires connected ie; pos neg. neg the tester onto any part of the vehicle chassis and the pos to the now live wire. Go through them all till all wires meet up. Now go on and extend the harness by means of soldering properly and insulating that wire from the main harness to the female fitting of the trailer connector. At each connection on the fitting fit on properly the different wires and do the same to the male connector from the trailer so that all lines up inside the two connectors. Good luck

You need a "test light". Then you turn on the circuit you want to wire in, tail lights, brake lights, blinkers and poke around the back of your light sockets until the test light comes on. Then you splicew into that wire and run it to your plug in. If you don't know which wire is what on the trailer, hook it up and with the wire fastened into the truck harness, try it on the trailer harness wires until you get the proper lights working. Process of elimination. Hope this helps.

is trailer lite fixture grounded good try and wiggle fixture when u hit signal. next try wiggle pig tail on trailer , still no signal. it must be wire from truck, trace back to connection and check all splices. to see if signal light works on trailer unhook pigtail and get a battery charger or another battery, connect a jumper from positive side to signal spot on trailer hook up. hook up ground as well see if light works if not its in the truck for sure.

Under the frame, your Sierra has a trailer harness. Locate it and hook up your trailer harness to it, every Sierra has a factory harness hook up in it, here is a link of your wire harness should be located under your Sierra.
Thank you for using fixya and good luck.
http://www.compnine.com/largeimg/970226TC02-230.gif

Advance and other auto parts sell a Hobie brand kit that simply plugs into the tailamp circuit. Follow directions supplied and you have trailer lights

taillights on what? Everything - needs to be grounded is the FIRST thing to remember. Try etrailers.com for parts or tech assistance or Google "Hoppy" trailer light kits.
Good luck

for your trailer you need park light, brake light, left and right signal light. the best way is to tap them in the rear tail light wires.

It sounds like your have may have your brake light and running lights crossed on your wiring harness to the trailer. Good luck and hope this help's

By an inline adapter, that goes between your main harness & tailights connection, and accepts flat 4 or whatever you require for trailer. Most automotive places have them, and perhaps even walmart.