I do not have left turn signal at the trailer plugs but have on the truck itself, is there a something I can do to get the left blinker on the trailer

There is a tail lights fuse for the truck, but not for the trailer.
First, check that your left tail light on the truck is working, if not fix the problem (new bulb, bad contact, fuse).
Then the obvious suggestions regarding the trailer are: Check the tail light portion of the bulb to be sure it is not blown. If good (best to put in new one to be sure), then check the wiring from the front of the trailer all of the way to the non working bulb, including every connection and at any place it is secured to the trailer frame. If all is good with the trailer circuit and bulb, then check the truck's trailer connector, including any adapters. If by chance the truck is wired with a flat 4 wire harness the problem may be solved (but usually the blinkers are the problem). Modern trucks require a 5 wire harness which self adapts to the standard 4 wire trailer circuit. Check for dc power (12 volts) from the truck's female connector. One wire will be ground, others will be taillights (turn on headlights), brake lights (have someone press brake pedal), and blinkers (turn on switch and blinkers).

If the trucks left side works, then it is a wiring problem. If it works at the plug(test light) then the trailer light has a bad ground. If it doesn't work at the plug, then it is a bad power wire from the turn signal wire to the plug. Some times it is the plug itself. Truck or trailer. Corrosion.

Hello Carol, The 7 way is for use with a brake controller and/or a trailer that has electric brakes. The 4 way flat is a basic trailer plug connector.
Connect as follows:
Green wire- Connects to the vehicles right turn wire harness & provides brake light and right turn signal on trailer.

Yellow wire- Connects to vehicles left turn wire & powers brake light & Left turn signal on trailer

White wire- Ground

Brown Wire- Tail/ marker/ license plate lights

The Blue, Red & Purple wires on the 7 way will not be used on the adapter, those are for brakes.

I hope this information is helpful.

it sounds that you have a voltage drop caused by bad wiring or a bad connection for the wiring of the trailer plug. you need to check the wiring of the trailer plug wiring back to were it connects to the truck wiring.pay attention to the condition of the plug connector itself.

On trailer plug, white is ground,yellow is left turn signal,green is right turn signal & brown is tailights.

You need to replace your turn signal switch in the steering colum I just bought one from GM they are about 300.00

You may want to get a ground loop isolator or even cheaper. Go to radio shack and buy two 1amp diodes and put them on each turn signal wire. This will eliminate the problem. The diode will be black with a gray line. the line will go towards the trailer on each wire. this should take care of the problem.

I take it the blinkers and brake lights work ok when not hooked up to the trailer? If yes, then the wiring to the tow hitch is not hooked up correctly. How many wires to trailer pig tail connection? U can have up to 7 depending on what you tow. Check to make sure these wires are hooked up from the truck to tow plug correctly: 7 wired---
brown-Rt turn and brake light, yellow-backup, white-ground, blue-electric brake, green-tail running lights, black-battery charger, red-left turn signal and brake light. Let me know if u have something other than 7 wire, I'll get the wiring color and source info for u.

brown to the tail lights. yellow to left turn signal. green to right turn signal. this is a basic 3 wire hook-up i use all the time w/4wire connectors for all trailers. white wire is not used. ground is established when you hook to the ball.
to find the correct wire to splice to, use a testor (has a clip to the bare wire, and a sharp point to the truck frame). using a needle, push it through a wire to rear light harness. turn on the turn signal. check if the connection is the blinker, testing until you have the blinker wire. the tail lights can be attached to the license plate wire. brakes and blinkers use same wire, so brake lights will work whenever the turn signal is attached.
to be sure everything is working right, have a second person go inside the truck and work the signals, brakes and lights one at a time while you are at the back of the trailer telling what to do.

exactly what does it do? please explain what happens when you press the brake turn on the light than brake signals ect.....