Problem with trailer lights when connected to one vehicle, but not another...

[nibs75]

Hi All, I've got a kind of confusing problem. At least it is confusing me. I've always towed my boat behind my Dodge Ram, and the trailer lights have always worked fine. My wife got a 4Runner over the winter, and I went to pull the boat out the other day with her 4Runner and no lights were working. I assumed her plug/wiring were bad or a fuse was blown. However, once I got out the test light, I am getting power at the plug for both turns, and tail lights (I couldn't check brakes as I didn't have anyone to push on them for me). I then plugged the boat back into the 4Runner, and tested if I was getting power on the other side of the boat plug, and am. I then hooked up to my truck to double check that something hadn't gone wrong.. all the lights work as expected when connected to my Ram. Though I did notice that if I have the L turn signal flashing, I see a very dim flash on the R also, and vice versa. Does this imply a bad ground or something? I've never paid that much attention to them in the past, but assume it's always been that way.

So to restate and be clear, all lights work when connected to the Ram. No lights work when connected to the 4Runner, but I do have power on both sides of the plug, even in the trailer wiring.. But no lights are coming on??

Could the Ram be supplying more power than the 4Runner, and maybe the 4Runner is not supplying enough? I mean the test light comes on, on the trailer side, but I've not checked right before the tail lights. I guess I'll go do that now.. Any ideas?

 

[oldjeep]

Re: Problem with trailer lights when connected to one vehicle, but not another...

Try jumping a ground wire from the frame of the 4 runner to the frame of the trailer. Or just use a continuity meter and see if you have ground continuity between the 2

 

[Bob_VT]

Re: Problem with trailer lights when connected to one vehicle, but not another...

Yup.......my 4runner is ground happy too. You also may have a faulty 4runner harness which is a plug and play adapter available at walmart.

 

[MH Hawker]

Re: Problem with trailer lights when connected to one vehicle, but not another...

Do both vehicles have the T harness connector. Those are designed to convert all of the different vehicale to a standard trailer wiring.

 

[Silvertip]

Re: Problem with trailer lights when connected to one vehicle, but not another...

Tail lights use a two-filament bulb. One of them is bright and one is dim. If the dim filament is flashing for the turn signal you have the wiring reversed. Turn and brake use the bright filament. If you and checking both sides of the plug on the toyota from the powered terminal to chassis ground you may have a bad ground in the white wire on the toyota. It is possible the ground (and a not very good one) is being made throught the coupler rather than the white wire on the truck.

 

[nibs75]

Re: Problem with trailer lights when connected to one vehicle, but not another...

Thanks for all the feedback everyone! I think it is a ground issue. I messed around with it a bit more last night, but got busy, so will try a few more things after work today. I'll let everyone know how it goes!

 

[nibs75]

Re: Problem with trailer lights when connected to one vehicle, but not another...

Just to close the loop on this thread. I ran a temporary ground line from frame of trailer to frame of truck and all light worked. Same for 4Runner. I traced the white wire back out of the plug on the trailer side and found a splice that could be seen down in the trailer frame where I couldn't get to it, so I clipped it and ran a new line. All is working as it should now! Thanks for the help and pointers!!