Tail light - driver’s side

[Gcc]

Hi all,

Used 2021 f150 - bought it a few months back. Was told my driver’s tail light wasn’t working last night when driving - the passenger’s side was on but not the driver’s side. But, it comes on when you apply the brake pedal. And it comes on when you lock the truck with the key fob. And it comes on when you unlock the truck with the key fob - except - it then turns off after a few seconds whereas the passenger side stays on with the rest of the lights for a much longer time. If it were the bulbs, seems like that wouldn’t happen. Any thoughts? I’m new to Fords and the F150. Thanks.

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[Kanuck]

XLT's come with halogen bulbs. Check to see if they have been changed out for LEDs. They maybe failing. You could try changing out the bulbs. Checking the connectors for dirt or corrosion would be another thing to check. Swapping taillights to see if the problem moves or not. After that, I would start checking for the correct voltages.

 

[DadBald]

There are high and low settings for the lamps, correct? So it sounds like your running lights are not working (lower output) but the brake light is working (higher output). Would you say this describes your situation?

If so, it's probably the lamps. I've seen them with 2 filaments inside the bulb before - one for running light (low output) and one for brake light (high output). The running light is on all the time with running lights, and both are on for brake lights. It's possible just the running light (low output) filament is burned out, so you'd need a new bulb. I'd pull the bulb and check it.

 

[HammaMan]

There are high and low settings for the lamps, correct? So it sounds like your running lights are not working (lower output) but the brake light is working (higher output). Would you say this describes your situation?

If so, it's probably the lamps. I've seen them with 2 filaments inside the bulb before - one for running light (low output) and one for brake light (high output). The running light is on all the time with running lights, and both are on for brake lights. It's possible just the running light (low output) filament is burned out, so you'd need a new bulb. I'd pull the bulb and check it.

Indeed. Locking I believe is brake lights vs normal illumination being parking/running lights achieved with dual filament bulbs (they're directional). If you ever see a car running down the road with one light brighter than the other they've installed one of these bulbs 180 degrees out of phase.

 

[Gcc]

Thanks. It looks like the Dealer has the right bulbs but they come in packs of 10....Do these go out that often that it requires that many on hand? Part number: JL3Z-13466-F looks like the right bulb. $56 for the pack. When I look at Sylvannia, they don't have 2 filaments like described above. These OEM ones do.

I can buy individual ones and have them shipped - but that adds shipping costs per bulb... not sure if that is better than just having them on hand....?

Thanks.

 

[Kanuck]

Thanks. It looks like the Dealer has the right bulbs but they come in packs of 10....Do these go out that often that it requires that many on hand? Part number: JL3Z-13466-F looks like the right bulb. $56 for the pack. When I look at Sylvannia, they don't have 2 filaments like described above. These OEM ones do.

I can buy individual ones and have them shipped - but that adds shipping costs per bulb... not sure if that is better than just having them on hand....?

Thanks.

Any auto part store will have them in single or maybe two packs. Also they be able to tell you the bulb number.

Brake light 3157
Turn light 3156 or 3157
Reverse light 3156 or 3157

These numbers should be on the bulb base

 

[DadBald]

You'll need one or two of each on the truck over it's whole life, just go to Napa or Amazon and pick one up

 

[Ford Motor Company]

Hi all,

Used 2021 f150 - bought it a few months back. Was told my driver’s tail light wasn’t working last night when driving - the passenger’s side was on but not the driver’s side. But, it comes on when you apply the brake pedal. And it comes on when you lock the truck with the key fob. And it comes on when you unlock the truck with the key fob - except - it then turns off after a few seconds whereas the passenger side stays on with the rest of the lights for a much longer time. If it were the bulbs, seems like that wouldn’t happen. Any thoughts? I’m new to Fords and the F150. Thanks.

Hello! Send us a private message with your VIN and current mileage. Allow me to see what I can do to assist. Thanks!

 

[Gcc]

So before buying bulbs I decided to swap one of the bulbs from the working side. I don’t think the bulbs are the issue. The bulb from the driver side worked fine on the passenger side and the bulb that worked on the passenger side did not work on the driver side.

So I tested the voltage coming out of the connector. When I unlock the truck with the key fob both sides flash but the passenger side stays on for a bit while the drivers side does not. Turns out I am getting a 12 volt reading out of two pins of the passenger side but not out of the driver side.

Here is the passenger side:

The two right pins have a 12 V reading for a little while after the truck is unlocked.

The bl/yellow is top and Orange/white is bottom.

This does not happen on the driver side. I get an initial voltage reading but then it goes to 0 when I probe those pins.

The pinout out of the colored wires is different but it is correct according to the limited wiring diagram I was able to find online. Ground (Bl/Y) and Vt/GN should give me 12V.

any thoughts? Does anyone have a wiring diagram more detailed than just at the tailight?

thanks,
Greg

 

[Gcc]

Hi all,

So an update...after checking the connector at the tail light and not seeing any voltage there, I was able to find a very basic wiring diagram and checked the voltage at the next connector down the line - connector c408 , which is under then truck. The Passenger side shows 12 volts there when I check (pin 26) but not pin 27, which is the driver's side. The next connector in line I should check is c3411. Does anyone know where that is? I can't find any any kind of connector diagrams that tell me where that is.

I'll probably have to bring it in, but...until I can I'd like to try and figure it out.

Thanks,

Greg

 

[Gcc]

Actually - I am not 100% sure the connector I checked was c408 - but it was the one under the bed of the truck under the tailgate. That one did not have voltage when it should have.

 

[Gcc]

So just to update….I found a diagram of the body control module and was able to check the voltage coming out of the bcm for that wire. It was sending out 12v when i tested it, so I figured I would have to find the connector in between the bcm and the one I tested yesteday. But when I put the bcm connector back on, the tail light started working fine. I dunno…I’ll keep an eye on it I guess. Weird.

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