No brake lights, turn signal or flashers.

[bdot0621]

I have a 2015 EL XLT and has been giving me hell with at first intermittent brake/turn/flash…now they have completely gone out. Bulbs are fine and even turn on the other filament that runs the rear lights in the back but the other filament never illuminates on both sides. Front turn and flashers work fine. I’m thinking the fets that control these lights are bad in the bcm. Can anybody help me with troubleshooting?

 

[Hamfisted]

I don't know if you have it already but here's the wiring diagram for the exterior lighting on the 2015-2017 Expy's. Has the Expy ever been wrecked in the backend ? I think you can see the BCM functions in ForScan on a laptop using the appropriate HS/MS OBDII adapter. Should show up on the MS bus, so put the adapter's switch in the MS position if it has one.

 

[bdot0621]

Yes it was hit and repaired in October of last year.

 

[Hamfisted]

Yes it was hit and repaired in October of last year.

Oh Ok. Well check the chassis grounds back there in the harness. Have you got up under the rear bumper area and looked at the repair work? Use a good flashlight and inspect the harness and the ground wire back there.

 

[bdot0621]

Man thank you! I’ve been dealing with this for a couple weeks and really need to get this resolved. I will take a good look tomorrow. Give u an update

 

[Fastcar]

If you have the plug for trailer lights it might be worthwhile to check there

 

[bdot0621]

All chassis grounds are corrosive free and are not frayed. Checked the harness and plug for trailer lights.

I’ve been looking at the diagram, could it be the FET in the junction box that went out? I’ve actually bought a bcm/junction box and replaced it. It’s used but the truck doesn’t start when it’s connected and I wanted to know if it needs to be programmed first. Thanks for any help

 

[Hamfisted]

Did you have trailer lights ?

2015 Expedition XLT Fuse Box on eBay





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[bdot0621]

Never used the trailer lights. How would I verify that?

 

[Fastcar]

Never used the trailer lights. How would I verify that?

You should have 1 or 2 receptacles to plug into. The wiring coming into them from the back may be at fault. You use a meter to determine if the signal is coming through the receptacle.