Bought trailer harness for my trailer all four poles show 4 wires mine has five wires going to trailer lights turn on signals both light up like four ways also no brake lights. made sure all lights were grounded

Sidelight, break light, turn signal. You can use a test meter to identify.

What is the color code for trailer wiring? On a 4-Way flat trailer wiring harness, white is the ground, brown is running lights, yellow is left turn signal and green is right turn signal.

Standard Color Code for Wiring Simple 4 Wire Trailer Lighting ...

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Rachel:

something is mis-wired somewhere... a trouble light or multimeter would be a handy thing to have right now. The four wires coming out of the plug are 1. ground. 2. left turn signal. 3.right turn signal. running lights. Ground the trouble light clip to some metal piece of the truck (the frame is best... make sure that the metal that you connect to is not painted or rusted. fire the truck up and turn on the headlights. Probe each of the connector contacts. the one that lights up the trouble light is your running lights on the truck's connector. Do the same with each turn signal. Left turn signal on... check the other three contacts in the connector. The trouble light will flash with your rear turn signal. Same thing with the right turn signal. Write down the colors of the wires and note which color corresponds to each function. Use your jumper wires to test the trailer plug. Connect the negative pole of the battery to the frame of the trailer with the negative jumper. Hook the positive jumper to the positive pole of the battery and connect a thin wire to the other end of the positive jumper. that thin wire will be positive or hot.... do not touch any grounded part of the truck with the thin wire... that means chrome trim, frame, or the ground wires from the plugs.
Now check to see which wire from the trailer plug is grounded to the trailer with a screw or nut and bolt. Do not touch that contact with the thin wire or you will blow a fuse! touch each of the other three contacts one at a time and observe which trailer lights comes on. Note which wires operate which lights. You will probably have to switch some wires where they hook up to the truck. For example, when you touch the blue wire contact with the thin wire and the trailer left turn signal illuminates, the blue wire to the truck needs to be connected to the left turn signal wire on the truck. Same with the right turn signal and running lights. Also check to make sure that the ground wire from the plug is a clean, tight connection at the truck and the trailer. sounds like a lot of work, but that is the only way that you will know that the rig is properly wired.

The universal harness with four wires assumes that the brake lights and turn signals use the same bulbs. If your Blazer has separate bulbs for rear turn signals and brake lights, this 'universal' harness will not work unless you buy a separate adapter to merge the power to the brake lamps and turn signals for the trailer.

Use a voltmeter and see which wires in the loom show power when (1) tail lights are on, (2) brake lights are on, (3) each turn signal is on, and (4) which shows continuity with vehicle ground/earth. Match these up with the appropriate wires in the trailer harness.
If your brake lights and turn signals are the same bulb on the towing vehicle, you're all set. If they are different bulbs, you'll need an adapter to get both brake lights and turn signals to work on the trailer.

I have the same problem.

First and foremost, installing the wiring harness is not the easiest task, but not the most difficult. Typically you will use a 4 pole harness. One wire goes to tail light on, second wire goes to brake light, then one to left signal and right signal. You will need a test light of some sort in order to determine the hot or live wire for each bulb. Once you confirm the wire you can simply splice the wire off the harness into the factory harness. One thing I will mention at this point is using a typical four pin instead of a adapter that are a it more expensive can cause more draw on your cars electrical system. Although I have never had any problems on my cars. I have heard situations in which wires have become cooked.

As far as trailer lights go it may depend on the state. Here in IL, you can get away with running 1 light on each side of the trailer granted all functions work-brake, running lights and turn signals.

Good luck

firat of all check and make sure you have a real good ground or otherwise you will lose current to another wire and this can short out and cause the lights to malfunction.

White: Ground
Brown: Running
Yellow: LT and Stop
Green: RT and Stop

This is the wiring code for the 4 wire trailers and
Wire a round seven-pin hitch, typically sold without a wiring harness, to the vehicle observing the following color codes: Run a white 10-gauge wire between ground and terminal one, run the blue 12-gauge wire between the electric brake controller and terminal two, the brown 14-gauge wire between the taillights and terminal three, the black 10-gauge wire between the permanently live 12-volt supply and terminal four, the yellow 14-gauge wire between the left turn/brake light and terminal five, the green 14-gauge wire between the right turn/brake light and terminal six and the purple 14-gauge wire between the backup light and terminal seven (in the center).

You need to purchase the trailer wire kit that has a solid state module that will allow the lights operate correctly. It plugs right in the factory socket, no cutting of wires are needed, and it costs around 40 dollars. It is the only way to go for your vehicle.

You will need a test light, don't worry about the colors. Four wires, one for left turn signal, one for right turn signal, one for parking lights, and one is ground(usually black). Hook up ground, turn on trucks left signal and hookup to one of trailers other three wires, you will either light up the correct light or wrong one just continue til lights match coming off your truck to what you want to light up. And brake lights are left and right signal, so if you do signals the brake light will work. I can explain further if you need help.

On the truck, are the turn signals and the brake lights using the same bulb, if the brake lights are using a different bulb the trailer might not work withe the truck if it only has a 4 wire plug, might have to add brake lights to the trailer and use a 5 wire plug, yes this means rewiring the trailer and adding lights