Tail lights - new issue - for me at least!

[3belkhunter]

Hello all,
Thanks in advance for what will undoubtedly be excellent advice and support.
I was coming home from a weekend away driving my 2019 F150 and it gave me an error message after an hour of highway travel that I need to service the left turn lights on the trailer (2010 Jay Feather Sport - 199). Sure enough when I got home and checked, the left 2 bulbs were not blinking with either the turn signal nor the emergency flashers. The lights on the truck were all working, and both bulbs looked intact. I suspect a wiring issue, but have never dealt with this issue and wouldn't know where to start. Thank you!

[Stainless]

First thing I would check is the plug connection.

[TCNashville]

You probably have 1157 bulbs in the tail light being it's 11 years old. With the lights on and the tail light cover off, jiggle the bulbs and see if they come on. Sometimes it's just a bad connection with the bulb and base.

[3belkhunter]

thanks, and I will check that, but weird both bulbs aren't working at the same time...

[RedHorse1]

Originally Posted by TCNashville

You probably have 1157 bulbs in the tail light being it's 11 years old. With the lights on and the tail light cover off, jiggle the bulbs and see if they come on. Sometimes it's just a bad connection with the bulb and base.

I have rescued a “dead” bulb by scraping the contacts with a knife to remove rust/corrosion. Dielectric grease applied over the contacts will help prevent the problem. Like TCN suggests it’s probably bulb/contact related. Let us know what you find. Your discovery/solution will likely help another board member (trust me ).

[Midnightmoon]

Could also be a bad ground to that light itself. Depending on how that trailer is wired, it could have ground wire coming off of the fixture or it could be grounded directly to the chassis if it is a post mount (those are more common on things like utility trailers however).

[JFlightRisk]

Turn signal, 4 way flashers, and brake light are all the same bulb filament and wire. Do the tail lights work on that side?

Another place to look, is the wiring junction box mounted on the frame. The wire may have come loose in there also. Original connections in there are with wire nuts, like in a house, and can come apart.

[3belkhunter]

After talking with a friend here in town, he suggested I check in the wiring box for a loose left side wire connection under the trailer. I'm also going to clean and lube (dielectric grease) the 7 pin connectors (male and female).

Will report back - I'm goin' in! Thanks everyone!

[TCNashville]

Thanks for the update, dielectric grease is your friend. I use it in most electrical connections.

[Jagiven]

Originally Posted by JFlightRisk

Turn signal, 4 way flashers, and brake light are all the same bulb filament and wire. Do the tail lights work on that side?

Another place to look, is the wiring junction box mounted on the frame. The wire may have come loose in there also. Original connections in there are with wire nuts, like in a house, and can come apart.

X2, If the brake light does not work, I would first suspect a ground wire issue. However, I do not suspect this is your issue as your TV, might indicate a failure with the brake light too. Usually if grounding is the issue, it is where the wire connects to the trailer frame. On your 2010, it is a fairly easy find. Lay on your back under the back of the TT, and look for a wire connecting to the TT frame. Remove, clean and reinstall. Easy check, with a multimeter. Check for voltage difference between the lightbulb socket and the TT frame (bumper), while power is supplied.

If it is only the turn signals (4Way and blinker send the power signal down the same wire). and determined it is not the light bulb or ground (easy check with a multimeter).

You could have an issue in a number of spots, I personally would start with the easiest things then work towards the harder items to check.

TT tail lights all have separate fuses inside the truck's fuse box. So, if you blow the fuse for the trailer's left turn signal fuse, the TV's left turn signal will still flash, and the trailer will not. Easy to check, grab your TV's owner's manual and inspect your fuses. The fuse boxes on most new vehicles are under the hood.

Simple test, grab a fuse holder with a 15 amp fuse, and jumper from AUX pin on your TT's 7 pin cord, to the left turn signal pin, if you blow the fuse, you know you have an issue with the left turn signal wire on the TT side. You can do this without a fuse holder and just jumper a wire across, but you can risk other issues, if you do have a wiring issue.

7pin wire connector, Check your pins, how dirty/oxidized are they? May need to be cleaned. Cleaning the connectors is not so easy. I would probably look at the next step, and come back if needed.

Wire connections at the end of the 7 Pin wire pigtail. This is where the black sheathed cable connects to the individual wires running though the TT. You may have a loose connection, water corrosion, etc. To locate the terminations, just follow the cable back. It may go to a metal electrical junction box outside your TT, or it may go through the floor into your TT (how mine is). I had one or two loose connections on mine that had to be redone.

If you do not find the issue, the root cause might be your TV.

[3belkhunter]

super detailed and helpful, although I'm not mechanically inclined - but these are great ideas that my son can assist me with - thanks and will update...

[3belkhunter]

Thanks all... So always check the easy stuff first, right?
I bought some CRC electronic cleaner and sprayed it in a few times and what do you know? It worked like a charm!
Next step is to add a little dielectric grease and I should be good to go... but I'm going to save all of the ideas everyone submitted for future reference. Thanks again!

[AndyO]

What did you spray, the bulb base, the chassis connection, or the 7 pin connector? Just to help someone else in the future maybe.

[jwhogle]

I had the same problem with my 2018 F250. Not a light bulb issue. The same warning came up with 3 different trailers (camper, boat and utility). It's a pin disconnected in the wiring before the 7 and 4 pin plugs. Ford dealer repaired in 10 minutes. In other words, don't waste your time, dealer will repair, I'm assuming vehicle is still under warranty.

[Midnightmoon]

Originally Posted by jwhogle

I had the same problem with my 2018 F250. Not a light bulb issue. The same warning came up with 3 different trailers (camper, boat and utility). It's a pin disconnected in the wiring before the 7 and 4 pin plugs. Ford dealer repaired in 10 minutes. In other words, don't waste your time, dealer will repair, I'm assuming vehicle is still under warranty.

Is that the connector up under the spare tire? I remember reading about that issue over on a Ford truck forum a while back.

[jwhogle]

IDK, I dropped the truck off at the dealer for an oil change along with a picture if the warning on the dash. i went to lunch...returned...repaired.

[lrousseau]

I’ve had the same problem in my 2014 Ford super duty. In troubleshooting everything and reviewing the owners manual, in the fuse block there is an independent fuse for the trailer wiring harness for the brake/left turn signal and the right brake/turn signal. This would apply to any trailer that you plug-in to your tow vehicles four-way or seven Way wiring connection. I would check for a blown fuse first.

[Quantum]

I would check this junction box at the front of your trailer (picture is upside down). I'm replacing mine with the one in the 2nd photo.

[Velz]

Originally Posted by JFlightRisk

Turn signal, 4 way flashers, and brake light are all the same bulb filament and wire. Do the tail lights work on that side?

X2`` Check the bulb and clean up the contacts. That's always been my experience with bulbs--especially on boat and utility trailers.

[ElRey]

Quantum - I need to replace/organize my junction box. Please supply a p/n and source of your junction box. The maze of wire nuts need to go away.