Trailer lights not working!?!?

I'm having the same problem as the OP with my 2006. No other fuses to be found anywhere. Trailer checks out as working on another vehicle. Used two different 7 to 4 pin adapters with no luck. 12v tester didn't light either. All fuses under the hood appear good. Don't think there's any in the cab that correlate to the trailer lights. Relay appears good. I sure don't know what to try now. Might be time to finally utilize that extended warranty that came with the truck....

 

I don't have anything like that in my frame either ('05 with factory tow package). Must have been something aftermarket added.

 

My 07 Pre-Runner has 3 fuses behind the left rear taillight assembly. Lower the tailgate, remove the two screws holding it in. Remove the light. In the picture you can see to the left of the large white bar code sticker there's a black box that controls the taillights. Below that box and the 2 white stickers, you can see the 3 fuses. On the right is the yellow 10 amp, to the left of that is an open slot that had a blown 7.5 amp, then to the left of that you can see the cover for the 3rd one.

 

My 2012 let me down the first time I tried to pull a trailer- no lights. Dealer found that the factory had forgotten to connect a plug somewhere. Lol

 

Not sure if this helps the situation, but, my 2004 DC had the exact same problem.

After some frustration and research I found and addition set of fuses for the trailer harness in the box behind the drivers side rear seat; never had those fuses fail again.

Cheers

 

I have a 2004 double cab with factory trailer harness. I have trailer light fuses behind the back seat drivers side, if that helps anyone.

 

On my 2002 taco extra cab 3.4 pre runner there is a power converter behind and under the drivers rear seat. There r fuses on the harnest leading to the power converter NOT on the converter. U have to pop the lil flip caps open to change them.

 

The trailer ground is not derived through the ball, unless you wired it yourself and did it that way. On either a standard 4 pin flat or 7 pin setup there is a dedicated wire for the ground. Typically, it is a white wire.

 

As usual, you guys are the best around! I don't know why I spend some much time investigating problems before I come here. I should come here to start with. My truck had been hit from behind a while ago, and when I finally hooked up a trailer, the tail lights didn't work. Brake and turn signals worked fine. I started tracing and checking power to the wiring harness and found that there was not power to the tail light wire where the harness plugs into the main system. I *finally* came here to see what the real experts had to say, and found out about the factory trailer fuses behind the drivers seat. And, low and behold, the 5 amp fuse was burnt out.
Thanks to everyone that pointed out the additional fuses.

Greg

 

Chiming in to say same thing happened here. Went to UHaul to pick up a trailer but lights were not working...well, I get right turn signal, but nothing else. Found one burned out fuse under the tow package black box converter thingy behind the drivers side back seat, and decided to replace all four 5A fuses just in case. Still no dice. Traced the wiring harness from trailer connector all the way back to cab, nothing looks odd or damaged. From what little bit I've see online, these mysterious black boxes are trouble, and hard/expensive to replace. Thinking of maybe just bypassing the lil' black box and tapping directly into tail lights for trailer hookup.

 

So I've got a little different issue but cant seem to find the problem. Ive got an 07 with flat 4 pin harness. Wiring on the trailer works great as tested with voltmeter and via friends 2012 Taco. Weird thing is when hooked to my truck, only the running lights work, not brakes or turn signals. All fuses have been checked good, except I cant find any of those hidden ones behind the drivers side rear seat. Ran a voltmeter to my 4-pin and strangely got erratic readings. For comparison sake we checked buddies truck, same erratic readings at the plug.

Im somewhat at a loss at what to check next..

 

Make sure your connectors on the trailer plug and on your truck are free from corrosion. I had this same issue and after cleaning those and checking the fuse box behind the seat and finding a few busted ones everything worked fine. Also get one of these. Very useful in determining if the issue is the truck or the trailer.

 

Thanks man! I did use a drill with metal brush to clean up the connectors and make sure everything was free of corosion, and all fuses are good. Except this behind the seat thing? I pulled back the seats but dont see any fuse boxes? Am I missing something obvious? ha

 

Did yours come with the factory tow package?

 

I'm not sure. I would guess it didnt, but I bought it used so I am not sure..

 

Hmm... Well if you can't find the trailer light box behind the seat you very well may not have it. At that point the only thing to do might be to follow the wires back to see if there are any issues.

 

I have a similar issue, but mine might be my trailer. I added a pair of taillights to my tractor supply trailer, and rewired to a regular 7 prong plug. The only thing that currently works is the additional lights I added which I connected to the full time on plug on the truck. As soon as I turn the ignition on, those lights go on, so I always have taillights, if nothing else. I do need to check all the other plugs to see if I am getting power, then start changing bulbs or going to LED lights on my utility trailer.

 

Ok sorry gmr102 Im an idiot. It is not factory tow package. After taking more stuff apart it is definitely an aftermarket harness with the converter box. Wires were spliced and soldered, and I think one may have been exposed due to old/cracked tape, and possibly shorting out. Just went through the whole harness and shrink wrapped the soldered parts and then zip tied everything up. Now just need to hook back up to the trailer and test, but its at a friends so that wont happen till tomorrow. Hopefully that was all it was. Thanks for your help!

 

I had the same problem as you, no factory tow package so had installed a little converter box when wiring several years back.


Similar to that.. couldn't for the life of me figure out why half my trailer lights were working and the others weren't... tried everything. Ended up cutting that converter thing out and wiring up a new one, and voila, everything worked.

Pretty sure moisture got into that box and messed something up

 

Oh awesome, that is good to hear. The one I have installed is the Hopkins set up. Ive re-done all the connections so when I get a chance to test again hopefully it works. If not, I'll just replace the whole system since its so simple. Cheers!