Question about 2003 Chevrolet TrailBlazer

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Left turn signal does not work on trailer

I purchased a tester because the left turn signal on the trailer did not work. when i connected the tester it did not work either. does anyone have a diagram of the wiring for the trailer harness on the vehicle.

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You might get lucky and someone will have them, but if not for 20.00 you can buy the complete service manual for your vehicle at, I use them regularly, if I already had a subscription on several cars but not yours, if I did I would be glad to email it too, I'm not sure you need a diagram to fix this though! I can tell you things to check. If you need me too, I am assuming you have checked your fuses for the trailer lights? and have tested that you are not getting current to the light?

Posted on Dec 23, 2008


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I have a 97 Ford aerostar van with tow package. when the head lights are on the trailer ligts are but turn signals don't work how do I fix this?

The turn signals don't work on the trailer or the van when trailer connected or turn signals don't work on the van without the trailer connected?

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I installed a new 7 wire connector on my wells cargo trailer, but when I connect the wires as per the color code the lights do react properly. Left signal works well, right signal flashes both tail lights...

Hi Bruce,

Let's back up for a second. Are you wired like this?

Using an inexpensive 12 V test light / tester like the one below, connect the clip to a good ground on the vehicle. Then with someone else working


the brakes, turn signals, lights, etc. ONE AT A TIME, you should push the point end of the tester into the corresponding connection on the VEHICLE. Only one connection should have power at any given time. Once you have verified that the correct & only connection has power at the right time - you can move to the trailer end of the wiring. If you can not verify the vehicle plug is working correctly - you'll have to get it working right before continuing. These connectors can develop problems over time and may need servicing.

If the trailer still has issues, check ground by uncoupling the trailer hitch from the ball on the vehicle. Keep the 7 pin connector from the trailer plugged into the vehicle and turn on the vehicle lights / have an assistant step on the brake. Connect the clip to the frame of the trailer and push the point to a good ground location on the vehicle. If the tester lights up - you have a bad ground wire between the vehicle wiring to the jack and the trailer frame somewhere. The lighting is relying on the contact between the ball & hitch for ground and could be causing the problem.

Check all the bulbs to make sure that they are the right ones and if the offset bayonet base type - inserted properly. Inspect lamp sockets, wiring and ground leads at each lamp socket. You can also disconnect a wire from a point that is common to left and right sides of the trailer to help narrow down where to look on the trailer for the trouble. If you disconnect a wire going to the left side and everything on the right works as expected when trying all the lights, brakes, etc. then you know the problem is probably on the left side. Reconnect the left side and disconnect the right side and test again. It is a process of elimination when you can't see anything obvious. Keep disconnecting 1/2 of the side that is causing trouble until you find the problem.

You can purchase a 7 wire vehicle jack test plug like this to quickly diagnose the vehicle for less than $10. It will indicate on the LEDs the power seen from the vehicle.


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1 Answer

I turn the left signal light on and it works fine, I turn the right signal on and the vehicle right blicks, but the left trailer blinks. All brake lights work. What is wrong? Ground connects are good

Who installed the wiring on the vehicle ( dealer, self etc.)
Was trailer wiring pre installed or someone else did it
How old is the trailer?
it seems that there is a bad connection on the vehicles wiring. perhaps wrong part was used or connection from vehicle right turn- to wiring harness is not hooked on properly. Depending on how confortable you feel, test to see if there is proper electrical current flowing to the wiring harness ( right turn, left turn, brakes, headlights) you should be able to detect which area on the harness does not get power when the vehicles right blinker is on. It is not too complicated, just requires deductive reasoning and a tester ( about $5 at Kragens) No harm will come to your vehicle's electrical system by doing this; worst case scenario: you blow a fuse.
If vehicle is working properly, it will be a bad connection on trailer

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I have the exact same issue. I have also tested my trailer on other vehicles and it works fine. I even purchased a light up tester and found the problem at the harness. It seems like a bad ground to me but I can't seem to find one.

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I have seen once before that the fuse box was bad on a 2003 Dodge 3500. I had power in and nothing out. We had to replace the box. Not cheap! Hope it is simple like a loose connection though. I think I had to pull the inner fender on the drivers side to access the bottom of the fuse box. Pain in the ****, but...

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Left turn signal on trailer

ok tdknutson, I'm not clear on this, does the truck left turn signal stop working when u plug the trailer in, or is it the trailer left turn signal that's not working, or both? When u plugged in the test light did it show u had power to that plug in? Let me know the answer to the above, and in the meantime, check the ground on the turn signal at the trailer. Make sure it's not loose, and tightly connected to the frame (or wire). Also, what type plug in do u have? 4, 6, 7 wire?

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