Trailer turn signals won't work

I have a 7 year old trailer that I'm working on. Replacing rotten wood, new wiring and taillight/turn signals that weren't working. The original 4 pin wiring does make the running lights come on but not the turn signal/brake lights. I also used a 7 way adapter with the 4 pin and only the running lights worked. I even ran the new wiring only to the tail lights and they still won't work. I cleaned and tightened the ground. Still no bueno. When I put a trailer tester in the 4 pin on my truck to check the lights it shows the running lights work but not the turn signals. It seems the truck is the problem. Fuses looked good. Has anyone else had this problem? If so how did you resolve it?

 

There are some trailer related fuses. Perhaps one of these is toast. I have used both my 4 and 7 pin outlets on my truck and they both work for turn and brake and running lights. I have used these on 2 different trailers.

I would start there and see if it a simple fuse issue.

Did you add anything to the truck that would involve disconnecting the trailer connection under the bumper?

 

did you check the trailer ground wire? I had a issue with an older trailer and that was it, got a fresh ground connection and everything then worked.

 

Definitely check the ground. And make sure that the trailer isn't relying on the ball/coupler for the ground.

 

^^

for sure, this through me for a loop many years ago, my dad had a Japanese built 4 runner that grounded through the hitch, I had a Taco that ground through the trailer, the TACO would not work, turned out the ground wire on the trailer was messed up.

 

Yeah I checked the ground. It was the first thing I checked. I haven't done anything to the trucks trailer connection. I looked under it wiggled it around and didn't see any issues. I did check the fuses. All appeared to be fine. I forgot to add in the original post that I have another trailer that uses the 7 way and connected to it after I did all this checking with the other one. The running lights and the rear lights would light up but the LEDs would not blink for turn signals. Thats when I felt that it must be a truck issue and tried the trailer connection tester. Which it failed that test also. I've owned both of these trailers from new and use them at least once a month and both were working fine until recently. The open trailer has regular bulbs that I would change periodically but I'm working with brand new lights that aren't working. Thanks for all the replies so far.

 

I haven't looked at my truck but I assume there's a connection point from the receptacle on the truck to the wiring harness on the truck. Maybe disconnect and reconnect?

Did you find a fuse specific for trailer turn signals? Without digging into the fuses on mine, I'm assuming that like other trucks I've owned, the trailer turn signals are on a separate circuit from the truck signals.

 

Fuses associated with towing circuits are in underhood fuse panel:

TOWING BRK 30A
TOWING IGR 7.5A
TOWING 30A
TOWING BK/UP 10A
TOWING TAIL 30A

Now if a fuse is indeed blown, there is a pinched wire, short to ground, or some other overload condition in the trailer itself somewhere.

 

Coming out of a 4 pin connector you should have
checking with a test light:

White ground
Brown tail/marker
Yellow left turn/brake
Green right turn/brake

 

A slick little LED tester plug can be found a Walmart or any parts store that plugs into truck connector that would confirm proper outputs...

 

Checked fuses all good and used a tester that showed only running lights no turn signals from the trucks trailer connector. I'll put it in the shop next week to have them diagnose it. Still under warranty. Appreciate all the help!

 

Another thought before you go to the dealer.... Did you test the tester on another vehicle to make sure it works? Sometimes the simplest things can get you.

Let us know what the dealer finds if that's the direction you have to go.

 

I'll try it on a neighbors truck when I get a chance. Need truck most of next week but will get it to the dealership probably Thurs. Will update the thread.

 

Update
While the truck was in the shop getting a brake kit installed ref squealing issue I had them look into the tow signal problem. They found a burnt fuse and that the trailer connections were getting power but did not have a way to verify signals worked without a trailer. Sadly I had to pay a $130 diagnostic fee. I had checked the fuses and didn't see any burnt but I'm not a professional mechanic! I used the trailer connection tester and it showed all lights should be working. I hooked up to my open trailer I'm working on and could get marker lights but no turn signals. I hooked up to my enclosed trailer and everything worked. I'm going to redo the ground connection on the open trailer and run new wiring that I already have and hopefully that will fix the problem All the old wood is removed so I'll be able to run it fairly easy.