Drivers Tail Light Running Lights Not Working

[AvockAdoo]

Did a bit of searching around here, and I cant find if anyone else has had this issue. I have the truck schedule in to see a mechanic in late April, but until them I'm running with a "burnt out" tail light.

Its my drivers tail light. Signal lights work, brake lights work, but the LED that snakes around the outside and acts as the "running light" at night is not working.

Its a 2020, has roughly 20k miles on it. I cant say I'm not disappointed that a truck this new already has an issue, but shit happens.

Food for thought - I had a topper installed about 2 months ago. I know it was working at that point, but I'm wondering if maybe the wires they tapped in the harness could be causing this? If so, I'm betting Ford will deny warranty and I'll have to fight with suburban toppers to get it sorted, but they've been good to work with so far.

Anyway, just posting to see if anyone else on here has had any issues where only one part of the tail light stops working.

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[Hedgie]

Not to be a smart ass, but have you check fuses?

 

[AvockAdoo]

I havent checked fuses - that would be a good spot to start. I assumed both running lights would be on the same fuse, but I could be wrong. I will check and report back.

 

[AvockAdoo]

Just read through the PDF of the manual, I cant seem to find one that would indicate left tail light specifically - maybe somebody else can weigh in.

 

[JDowns]

There are no fuses for your issue. The lights are fused via FET's in the BCM.

You could and should before you take it in for service disconnect the topper light connection at the brake light(s).

The BCM may reset assuming it hasn't triggered enough faults to require a dealer reset. The BCM keeps a counter per circuit for every fault. If the number exceeds a programmed threshold the circuit is disabled in order to prevent damage to the BCM. The dealer has to go through a checklist to ensure the circuit is good in order to reset the circuit on the BCM.

If there is now a fault with the BCM and needs to be replaced the dealer can deny warranty due to a third party component being tapped into the circuit. Which is why its advisable if you tap into any circuit related to the BCM you use a proper "Y" harness to quickly return to stock to avoid any warranty issues.

 

[AvockAdoo]

Jeff - I really appreciate your input. I am taking the truck back into where the topper was installed today for them to do a check on it, but maybe I'll ask them to pull the wiring harness that they installed out. I will disconnect the topper at the quick connection now and see if that fixes the issue temporarily or not.

 

[AvockAdoo]

Also - is this something I could (or maybe shouldn't) try to look at or reset using FORSCAN? I am not interested in the potential of causing any (more?) damage than what has been - hopefully the BCM will reset its self on my drive over.

 

[JDowns]

To reset the BCM (not a full dealer reset as that is done programmatically) you need to do a full key on off reset. Key off and allow the power hold feature to end. This typically takes 5 minutes. Then turn back on and if the BCM circuit resets the lights should work. Hopefully its just temporarily disabled and doesn't require a dealer visit, best of luck.

 

[JDowns]

Also - is this something I could (or maybe shouldn't) try to look at or reset using FORSCAN? I am not interested in the potential of causing any (more?) damage than what has been - hopefully the BCM will reset its self on my drive over.

I'm not aware of any documentation on how to do the reset via FS. There are numerous circuits / counters within the BCM. How it was explained to me is there is both a manual and diagnostic checklist that has to be performed before the circuit can be reset. You would have to find the bits with FS that identify both the counter (reset to zero) and the flag to enable the circuit.

Regards,

 

[AvockAdoo]

Sorry if I'm sounding a bit dense - but I want to make sure I'm tracking with what you're saying about the key on-off reset. Basically, key on, and then off. Wait 5 minutes (at least) and then turn it on again? Seems like this is something that happens essentially every time I drive the truck anywhere.

 

[AvockAdoo]

Sorry for the double replying as well - from some other reading, I think I'm going to have them re-run the connection to the trailer lights connector, as those are fused separately and NOT through the BCM. Sounds like a safer alternative. Hopefully they can cover their tracks well enough (and I get a kind enough service advisor) if I do need to take it into Ford. Who knew a topper install would create so much headache! Cant stress enough how easy suburban toppers has been to deal with. Even through all of this they are being beyond helpful.

 

[JDowns]

Sorry if I'm sounding a bit dense - but I want to make sure I'm tracking with what you're saying about the key on-off reset. Basically, key on, and then off. Wait 5 minutes (at least) and then turn it on again? Seems like this is something that happens essentially every time I drive the truck anywhere.

Yes. Depending on the situation, key left in "ACC", etc. No change would be observed. Just highlighting in order for the BCM to reset a full key on off cycle has to be done. I'm assuming this is a power saving feature.

When I say BCM reset its actually a restart of the computer.

 

[JDowns]

Sorry for the double replying as well - from some other reading, I think I'm going to have them re-run the connection to the trailer lights connector, as those are fused separately and NOT through the BCM. Sounds like a safer alternative. Hopefully they can cover their tracks well enough (and I get a kind enough service advisor) if I do need to take it into Ford. Who knew a topper install would create so much headache! Cant stress enough how easy suburban toppers has been to deal with. Even through all of this they are being beyond helpful.

It's generally a bad idea to draw excess current from a component through the BCM. Especially LED's without a constant current driver.

You could draw power from the rear bed lights / power connector (fused) and use a relay tied to the brake lights. That would achieve the same result. Power to the topper lights only when the tail lights are on. By using a relay the amp draw for the relay is very low and shouldn't effect the BCM circuit. This is how the factory tow controller is wired somewhat. The cargo light brake light is tapped as a signal wire for a relay. There is a separately fused tow circuit that is used for main power draw.

No worries on the double reply. I do that all the time, especially when I'm low on caffeine.

 

[AvockAdoo]

Disconnected the battery for 15 minutes, plugged it back in, and we are back in business (without the topper brake light connected).

Ill have them tap the brake light from elsewhere. So glad to have not brought this into ford yet.

 

[JDowns]

Disconnected the battery for 15 minutes, plugged it back in, and we are back in business (without the topper brake light connected).

Ill have them tap the brake light from elsewhere. So glad to have not brought this into ford yet.

Glad to see your back in business. They can still tap the brake light from there or the trailer harness. Just use a separate power source and the brake light as a trigger for a relay. Multiple other ways of doing this safely without drawing full current for the lights on the dedicated BCM circuit. Not sure if the trailer harness has current sensing and would think a trailer is connected though. I would test before I buttoned everything up though.

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