Left rear turn signal/brake not working?

BRIANSCOTTCOLE

MEMBER
2011 FORD F-150
5.0L
V8
4WD
AUTOMATIC
360,000 MILES

My left rear turn signal/brake doesn't work. Replaced bulbs and checked all fuses and relays. The front left works so I don't think it is the multi-function switch because I have read that it just does each side not each corner individually. I have also read that it could be the BCM. I bought a code reader and don't have any codes. I disconnected the battery to reset ECM. One question I have is if the top bulb or socket is bad on the rear left, does the bottom not work? The other question is, will a faulty BCM always give a code?

7 Replies

MIKE H R

MECHANIC
3,094 POSTS

Most times I find out that there may be a wire that is worn and not getting the voltage for the brake light, check the connections for the light wires. Does the front signal flash faster when the back one is not working? I would guess it is in the wiring near the back of the truck. Does it have a towing package? Thinking it is in a loose or broken ground wire. Turn the signal on and check the wires with a static tester. That would let you know if it is getting voltage to the socket. Let me know what you find.

Mike

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Wednesday, March 29th, 2023 AT 6:20 AM

BRIANSCOTTCOLE

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4 POSTS

Yes, the front is blinking faster. Question: if the trailer light wiring harness is faulty, could that cause this issue with the rear left light?

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Wednesday, March 29th, 2023 AT 8:53 AM

MIKE H R

MECHANIC
3,094 POSTS

It could be the problem, check the wiring for the trailer lights. Most times I have seen where a bad connection or burnt out bulb will make the flasher flash faster without the burnt out on not working at all. Make sure you check the wires that are connected to trailer plug are clean and not shorting out
Mike

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Friday, March 31st, 2023 AT 9:48 AM

JACOBANDNICKOLAS

MECHANIC
109,755 POSTS

Hi,

I noticed we haven't heard from you for a couple of days. Have you been able to make any progress?

Also, if you haven't already, check to see if there is power to the signal bulb connector when the light is requested.

Let me know.

Joe

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Sunday, April 2nd, 2023 AT 7:19 PM

BRIANSCOTTCOLE

MEMBER
4 POSTS

No power to the lights. I have an appointment 4/5 to get it diagnosed at a local mechanic. I checked the plugs near hitch receiver and above the spare tire and couldn't find anything.

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Monday, April 3rd, 2023 AT 4:39 AM

BRIANSCOTTCOLE

MEMBER
4 POSTS

No power to the lights. I have an appointment 4/5 to get it diagnosed at a local mechanic. I checked the plugs near hitch receiver and above the spare tire and couldn't find anything.

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Monday, April 3rd, 2023 AT 4:40 AM

JACOBANDNICKOLAS

MECHANIC
109,755 POSTS

Hi,

Okay, if the front work, fuse 14 at the body control module is good. However, there are two different wire feeds to power the front and the rear.

At the body control module, there is a gray wire that feeds power to the left signal and brake lamp. (See pic 1) We need to check if there is power present there for the two lamps. If there is, then we have an open circuit between the BCM and lamp assembly.

Let me know if this is something you feel comfortable doing. Hopefully, we can save you the labor bill on the 5th.

Take care,

Joe

See pic below.

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