2017 F150 XL 4x4 3.5 NA 30k

The rear driver side brake light and turn signal aren't working. Hit the brake pedal nothing, turn on the turn signal nothing. But when I hit unlock on the key fob the light flashes like the other so the bulb is good. (swapped it anyway just to check)

Thoughts?

 

Still under warranty? I see you only have 30k on it so s long as time hasn't run out I would let the dealer fix something like that.

 

Where's the fun in that?

That is definitely an option- just curious if anyone else had a problem similar to this, if it's a simple fix I'll probably just do it myself.

 

Totally get that!!

The only reason I would say dealer is because electrical isn't like it was 20 years ago. Everything is controlled by this module or that module and unless it is a simple ground issue, very possible, it wouldn't be to difficult to mess one of them us.

 

Yeah the fact that it lights up when unlock the truck seems to indicate that the wiring is ok.

 

You can always try the restart....disconnect your battery for ten minutes and see if that fixes it.
I don’t know why it would help, but it’s odd how electronics sometimes respond to that.

 

Good suggestion! Kind of like a "three finger salute" in Windows. If at first you don't succeed, reboot the darn thing!

 

Well that would be an easy place to start, mine as well clean the terminals while I'm there.

Good call, will post results.

 

If it were an older car, I'd suspect that the fob is flashing the low (marker) circuit, not the high (brake/turn) circuit. I haven't messed with this on this new of a vehicle, but if something is disconnected toward the brake/turn lights and not the markers then this would explain the symptoms.

 

Sorry for the delay been busy with other things and I usually drive another vehicle.

Here's the new info-

If you turn on the driving lights the bulb is lit.

If you key the fob the bulb is lit.

Put hazzards on and no light.

Apply brake and no light.

Socket is standard push in with terminals on either end, a positive and a negative. Going to the socket are three wires, not two.

When applying the brake etc there is no voltage to the terminals at the socket (bulb pulled metering the socket direct)

When keying the fob etc the terminals show voltage.

SO-
Here is my theory so far:

At indicator or brake on situation there is no voltage at the socket. There are three wires to the socket which I assume (I know) are negative/common, power on from running lights, fob etc, and 2nd power on from brake, turn signal.

1) All systems are normal, when the brake or indicator is applied the brain is sending power to the socket but a brake in the wire etc is preventing it from arriving at the socket.
2) There is a module/relay/widget somewhere not sending the power when it is supposed to.

Tried resetting by disconnecting the battery for almost an hour, no change.

Owners manual does not seem to clearly identify a fuse for this circuit and even if it did unlikely that just this leg would be affected and nothing else.

Thoughts??

 

Just a thought. Is the proper bulb in the taillight?

 

Good question: yes.

Initially thought probably just a bulb so bought new, same symptoms so exchanged new bulb with bulb from passenger side. New bulb works properly in passenger side and bulb from passenger side acts the same in driver side.

 

Definitely sounds like there’s an issue with the harness.

With newer vehicles, chasing down electrical problems can be a PITA.

When you have time and since it’s under warranty, take it in to your dealer and let them deal with it.

 

And there's the rub- thought I was good, and still under the powertrain but just past the bumper to bumper.

 

Do you have a camper shell? I've heard some splicing and adapters for aftermarket light accessories can cause quirky issues? Anything aftermarket electrical?