2008 chevy trailblazer trailer lights not working

[ggundersen3]

Just traded in a 2004 Chevy Trailblazer on a 2008, basically the same vehicle. I tow a 19' bow rider with it. Trailer lights always worked fine on the 2004. The receptacle on the back of the '08 is dead. I checked all the trailer light fuses in both the underhood and under the rear seat fuse box. All good. Any ideas where my problem is???? I used a tester and there is no power to any of the pins in the receptacle. Looking for ideas for the next thing to check. Thanks.

 

[gm280]

Not sure how yours is wired, but that fact that everything on your trailer is not working suggest a common ground issue with the vehicle. I would check to make sure you have a workable ground on the vehicle for starters. Take your voltage reading from both the chassis AND the trailer plug to verify you have voltage when turned on. If you lack any voltage to either grounds, then you have to either get the wiring schematic of your vehicle or trace the actual wires back to the problem(s). Hard to believe you have all the trailer system wires with blown fuses. It has to be something common or not turned on or such.

 

[ondarvr]

I had 3 Trailblazers, the only issue I had with trailer lights were the fuses, and since you found both fuse boxes and checked them I don't have much to say. If I remember correctly there are separate fuses for turn signals, break lights and driving lights., so it would need to be something common to all of them. GM trucks from that era were known for electrical problems though.


Was there power at the fuses?

 

[Silvertip]

Perhaps the trailer harness plug became disconnected as the result of prior body work or due to an accident.

 

[ggundersen3]

I'll check the vehicle harness after unplugging from the side connector/plug.

 

[gm280]

Like ondarvr stated, GM does some wacky wiring and every little light has its own fuse. Even the separate license plate lights. The left one has a fuse and so does the right one... So every light that goes to the trailer also has individual fuses. and there is a common larger fuse that goes to all those lights and if I remember correctly, that is located in the under hood power distribution fuse box. So it is either a harness disconnected or a main fuse blown. I actually bought all the factory shop manuals for my '98 Blazer so I know how crazy they wired things. Use a meter to verify a fuse is good or blown. Take each fuse out and ohm it to verify it is good. A customary look doesn't work all the time. Neither does a check across the fuse. You have to isolate the fuse and ohm it in older vehicles to make absolutely sure... I learned that the long way myself!

 

[ggundersen3]

Thanks gm280! You are so right about the wacky GM wiring/fuses/fuse boxes/lighting. So after further checking using my tester, I discovered the vehicle side connector is not entirely dead as I stated earlier. I had the ground clip on the wrong pin. Using the correct pin for the ground, it showed the turn signal pins working, and brake light pin now working, however the same pin as brake lights was hot when only tail running lights were on. That's not right? And the "round to flat" adapter is completely dead when plugged in. So, I'm thinking I have 2 things wrong. 1)a bad round to flat adapter and 2)a bad vehicle side connector

 

[ondarvr]

Part of the issue can be the plug on the vehicle, each socket can become corroded and the round to flat adaptor won't make contact in all or some of the sockets.

Try grounding to the frame and see if you get a different result, sometimes a sign of a bad ground is the lights working odd in or not at all in some combinations, like applying the brakes or activating the turn signal while other lights are on.

 

[ggundersen3]

Thanks