My trailer's left turn signal/brake light and right rear parking light doesn't work. All lights work on the truck and all other lights work on the trailer.

I plug this trailer into the 4 pin connector on the factory towing package. In addition, I towed with my friend's trailer using the 7 pin connector and the exact same thing happened, so we can rule out the trailer and the connector (I doubt they would both have the exact same problem).

The thing that gets me is the parking lights. I'm assuming the trailers have the same circuit for all of the parking lights, so why would one just not work?

Are there any fuses I should check? Could a bad relay cause this? I bought this truck used, so I am unsure about the relays themselves.

 

You can't get around the fact there is only one wire for both parking lights. Could be both trailers do have the same parking light out. If you have the factory tow package you will have a fuse for left turn/brake and one for rt turn/brake. These are sep from truck light fuses. You could blow one of these and affect one side of the trailer turn/brake lights but not the truck. these fuses are under the hood, driver's side.

 

the trailer lights have separate fuses to the trucks lights and left and right are also separate. the fuses are in the power distribution box under the hood.
Fuses # 5, 19 and 20

 

I checked 19 and 20 and they're fine, I will check #5 tonight.

I also found out that the relays weren't installed. It still baffles me that they wouldn't take the 5 seconds to install those.

 

If checking the fuses doesn't yield an answer, here are a couple things to think about. Did this just happen or has it always been that way?

First, are you absolutely sure that the plug on the truck is all factory? It could be the factory plug and still a hack job wiring if the previous owner went to the dealer and asked for a trailer plug. I think the harness and plug come as separate pieces but don't quote me on that. Next find a multimeter and check the plugs. Make sure it's not some strange contact problem.

The parking light thing confuses me. The golden rule with trailer wiring is to check the ground because 90% of all problems are a result of a bad ground. This could be a bad ground on the trailer or the ground from the trailer to the truck. I have seen the bad grounds cause a trailer light to look like it is completely out but if you pull the cover off the light and look really close it will be so dim as to be unrecognizable through the lens.

Hope something here helps,

WV

 

I checked #5 and the fuse is still good. I will bust out the multimeter sometime soon, I just hate tracking down electrical gremlins in cars, drives me bonkers. After you've done this to a racecar (http://www.nissanperformancemag.com/september05/g20/), you never want to see another wire again.

I am certain it was factory installed. It's on the window sticker and has the connector and everything (no splices). Factory tow hitch and tranny cooler as well.

Your theory on the ground sounds good. Could be that on both trailers the pass side light is "last" on the loop and just doesn't have any juice left.

If it's somewhere in the harness before the plug, I'll just drive the thing off a cliff...

 

That may be a little extreme but I understand the sentiment.

WV

 

BTW, I fixed the link to my racecar...

 

Fixed the problem. When I plugged in the relays for the reverse light and trailer 12V, for whatever reason it worked. I didn't think that those would have anything at all to do with them, but I'm not complaining...

 

I agree they shouldn't have anything to do with it, but I'd take it. Thanks for reporting back for the next guy.

 

No problem sir...