Bed light not working all the sudden

Kgorman

Tremor Fanatic
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Location
Texas
Current Ride
2020 F250 Lariat Tremor 7.3
Went out tonight and was going to install builtright panels but the bed lights don’t work, they did last night and I haven’t touched it all day. The overhead lights on the cab illuminate but not the ones at the end of the bed. Neither right nor left. Inside button or outside button in the bed same story.

anyone seen this before?
 
Fixed!

for whatever reason the BCM that controls the lights told them to stay off. A reset of the BCM by removing the negative battery terminal for 10 minutes fixed it.
 
Fixed!

for whatever reason the BCM that controls the lights told them to stay off. A reset of the BCM by removing the negative battery terminal for 10 minutes fixed it.
Good info, I would have thought a simple blown fuse at first. I need to get a copy of the uncompiled software for this truck to figure out some things... I have a couple of good friends that work for Ford as engineers, I'll see if I can score a copy to assist with these 'odd' troubleshooting issues. I doubt that I can get that, but it would totally be the ultimate score because then I could literally change anything I wanted and not be limited to ODBC allowed functions. I can dream.
 
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Fixed!

for whatever reason the BCM that controls the lights told them to stay off. A reset of the BCM by removing the negative battery terminal for 10 minutes fixed it.
I had the same thing happen in my 14 F150 after I started swapping in LED lights everywhere....I never got them back.....
 
I don't like that they don't automatically turn on when I open the tailgate.
You could always add a magnetic switch and wire it to power the light when contact is not made. The switch on your light would need to remain in the "ON" position.
 
Dug up this old thread cause I am having the same issue, bed lights aren't working. Anyone know if there is a method to reset the BCM using FORSCAN?
 
Dug up this old thread cause I am having the same issue, bed lights aren't working. Anyone know if there is a method to reset the BCM using FORSCAN?
Curiosity: Was the truck dormant for any length of time? If the battery drops below a certain point, it will start to disable some functions. When this happened to me, I started the truck, let it idle a bit, shut it off and the bed light worked again. It happened several times in the past because I do not use this as a daily driver. So, I installed a NOCO trickle charger to keep the battery full at all times and now the bed light works every time, even after sitting a week.
 
Curiosity: Was the truck dormant for any length of time? If the battery drops below a certain point, it will start to disable some functions. When this happened to me, I started the truck, let it idle a bit, shut it off and the bed light worked again. It happened several times in the past because I do not use this as a daily driver. So, I installed a NOCO trickle charger to keep the battery full at all times and now the bed light works every time, even after sitting a week.
Actually yes, more than it has been since I brought it home last April. It’s been sitting most of the week, which I wouldn’t think would have any affect, but it usually gets driven daily.

I tried the battery disconnect but still no bed lights. I take it for a ride tomorrow and see if that fixes it, really don’t want to take it to the dealer…but if it sitting for a week causes this then potentially something else brewing. Figures after I didn’t get the bed light with the DB cover.
 
Actually yes, more than it has been since I brought it home last April. It’s been sitting most of the week, which I wouldn’t think would have any affect, but it usually gets driven daily.

I tried the battery disconnect but still no bed lights. I take it for a ride tomorrow and see if that fixes it, really don’t want to take it to the dealer…but if it sitting for a week causes this then potentially something else brewing. Figures after I didn’t get the bed light with the DB cover.
It may not be a problem. There are numerous stories in here on this subject. Many have added battery maintainers to keep their batteries charged while sitting. If the battery drops below a certain level, the truck may go into the sleep mode to protect from over discharge, which disables convenience functions. Check a few strings on this forum with key words, sleep mode, NOCO, chargers, etc. Here's one below.

 
My Tremor lIves indoors for most of the week, and being an RV’er, m/c rider and Boater, I’m used to having the trickle chargers on my stuff. One of the first things I set up for it was the NOCO Charger. Great item! 👍
 
Fully charged the batteries and checked Forscan for any potential codes, still nothing. No idea when they actually stopped working, wasn’t trying to use them much prior to now, figures.

Anyone got any ideas on things I can check/try before I take it in?
 
Fully charged the batteries and checked Forscan for any potential codes, still nothing. No idea when they actually stopped working, wasn’t trying to use them much prior to now, figures.

Anyone got any ideas on things I can check/try before I take it in?
Sorry to hear you are still having issues. At this point, I would be checking voltages but not sure that is something you would want to do. The BCM could have a problem, I assume it doesn't work from either switch, in cab or in the bed? Do the lights come on if the truck is running?

Here's some irony for you: After reading your reply, I just went out to see if my in-bed lights still operated, truck was not run for about a week with the NOCO trickle charger plugged in. They didn't light up! But the rear cab light (or bed light) did. So, I popped a voltmeter into a known hot socket that I installed, and the battery voltage was at 12.4 volts. The in-bed lights did not come on with either switch, in cab or in bed actuated. So, I started the truck while the rear cab light was on. Voltage instantly went to 14.4 volts and the in-bed lights came on. I ran it for about 10 minutes and shut it off. All the lights now act normal, and the battery voltage was at 13.3 and dropping. (Should drop to about 12.7 volts when the charge neutralizes.)

So, two things I learned here. My 2-amp NOCO charger is not adequate to keep the charge up when temperatures drop, (been in the low 30s lately) and the rear cab light and in-bed lights have their own feed in spite of coming on at the same time when the button is pressed.

My batteries are not at full capacity at 1 year old now, however load testing says they're still good. But to have the problem at 12.4 volts tells me they need to be up higher to keep the truck operating normal. I still may need to replace the batteries but for sure, I need at least a 5A trickle charger for the current ones.

No codes were ever generated. Hope this helps.
 
Sorry to hear you are still having issues. At this point, I would be checking voltages but not sure that is something you would want to do. The BCM could have a problem, I assume it doesn't work from either switch, in cab or in the bed? Do the lights come on if the truck is running?

Here's some irony for you: After reading your reply, I just went out to see if my in-bed lights still operated, truck was not run for about a week with the NOCO trickle charger plugged in. They didn't light up! But the rear cab light (or bed light) did. So, I popped a voltmeter into a known hot socket that I installed, and the battery voltage was at 12.4 volts. The in-bed lights did not come on with either switch, in cab or in bed actuated. So, I started the truck while the rear cab light was on. Voltage instantly went to 14.4 volts and the in-bed lights came on. I ran it for about 10 minutes and shut it off. All the lights now act normal, and the battery voltage was at 13.3 and dropping. (Should drop to about 12.7 volts when the charge neutralizes.)

So, two things I learned here. My 2-amp NOCO charger is not adequate to keep the charge up when temperatures drop, (been in the low 30s lately) and the rear cab light and in-bed lights have their own feed in spite of coming on at the same time when the button is pressed.

My batteries are not at full capacity at 1 year old now, however load testing says they're still good. But to have the problem at 12.4 volts tells me they need to be up higher to keep the truck operating normal. I still may need to replace the batteries but for sure, I need at least a 5A trickle charger for the current ones.

No codes were ever generated. Hope this helps.
Just to make sure I’m pushing the right buttons, the interior switch is the one lower left on the headlight selector switch correct?

Oddly enough that switch (interior)didn’t seem to do anything for the cargo light, the light integrated with the third brake light. It wouldn’t turn it on and when I open the doors or unlock the truck, it won’t turn the light off either. Didn’t seem to do anything all. I will attempt to check voltages if I have sometime tomorrow or Friday. The batteries are factory and it was built Feb/Mar of last year so maybe 🤷🏻‍♂️.

Thank you again for the insight.
 
Just to make sure I’m pushing the right buttons, the interior switch is the one lower left on the headlight selector switch correct?

Oddly enough that switch (interior)didn’t seem to do anything for the cargo light, the light integrated with the third brake light. It wouldn’t turn it on and when I open the doors or unlock the truck, it won’t turn the light off either. Didn’t seem to do anything all. I will attempt to check voltages if I have sometime tomorrow or Friday. The batteries are factory and it was built Feb/Mar of last year so maybe 🤷🏻‍♂️.

Thank you again for the insight.
Yes, the cargo light switch in the cab is on the panel as in the #1 picture. There is a sequence to be considered, you're describing a normal situation. I tested this with the battery in the charged state.

The sequence I tested is as follows:
Open Drivers side door: #2 picture (cargo light is on, running lights on, no bed lights on)
Press switch in bed or on dash: #3 picture. (Bed lights and cargo light stays on.) (Tail gate is open to observe lights)
Press switch on dash or in bed: Bed lights go off, cargo light stays on.
Close the door: 15-20 seconds later, cargo light goes off.
Press lock on handle with door closed at any time: all lights extinguish except the bed lights and cargo light if they were in the ON position via the buttons. After several seconds, they also extinguish.

These lights are directly controlled through the BCM and if it still doesn't work out. it probably needs factory service. The lights are FET controlled through a microcomputer. Measuring voltage would be tricky at best if you don't know what you are looking for. FYI, the "hot" wire for the bed lights is white and the negative lead is blue and grey, which turns into blue and brown, which eventually turns into blue at ground.

From the service manual:
Demand Lamps
When the BCM is in not in battery saver mode, the interior light output is energized to provide voltage to the demand lamps.
The cargo, truck bed and trailer assist lamps all illuminate with the courtesy lamps. They can also be illuminated by using the cargo lamp switch
(integrated into the headlamp switch) or the truck bed lamp switch, located inside the LH rear of the truck bed.
 

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Yes, the cargo light switch in the cab is on the panel as in the #1 picture. There is a sequence to be considered, you're describing a normal situation. I tested this with the battery in the charged state.

The sequence I tested is as follows:
Open Drivers side door: #2 picture (cargo light is on, running lights on, no bed lights on)
Press switch in bed or on dash: #3 picture. (Bed lights and cargo light stays on.) (Tail gate is open to observe lights)
Press switch on dash or in bed: Bed lights go off, cargo light stays on.
Close the door: 15-20 seconds later, cargo light goes off.
Press lock on handle with door closed at any time: all lights extinguish except the bed lights and cargo light if they were in the ON position via the buttons. After several seconds, they also extinguish.

These lights are directly controlled through the BCM and if it still doesn't work out. it probably needs factory service. The lights are FET controlled through a microcomputer. Measuring voltage would be tricky at best if you don't know what you are looking for. FYI, the "hot" wire for the bed lights is white and the negative lead is blue and grey, which turns into blue and brown, which eventually turns into blue at ground.

From the service manual:
Demand Lamps
When the BCM is in not in battery saver mode, the interior light output is energized to provide voltage to the demand lamps.
The cargo, truck bed and trailer assist lamps all illuminate with the courtesy lamps. They can also be illuminated by using the cargo lamp switch
(integrated into the headlamp switch) or the truck bed lamp switch, located inside the LH rear of the truck bed.
So uhhh, I fixed it. Apparently something I did within Forscan disabled the bed lights inadvertently. I believe it was related to my shenanigans when trying to get the global open/closure stuff to work. I did an "as-built" reset and they work now. Went back through and just added a few adjustments (TPMS, double honk removal) and they are still working.

I appreciate your assistance in troubleshooting @Canyon Trekker!
 
Need Help....... I'm still digesting all the controls on my new 2024 F350. I can't find the exterior bed switch to turn on the bed lights in the rear corners above the power port and the 5th wheel connector. The push button switch in the rear (above the 5th wheel connector next to the light) turns on the bed cargo lights but the two vertical bed lights in back are a mystery. Can anyone tell me what external switch is supposed to turn them on and where it is? I realize I can turn them on from the instrument panel cargo light switch. Please don't tell me that I need to open the truck if I'm already out to turn them on.
 
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Need Help....... I'm still digesting all the controls on my new 2024 F350. I can't find the exterior bed switch to turn on the bed lights in the rear corners above the power port and the 5th wheel connector. The push button switch in the rear (above the 5th wheel connector next to the light) turns on the bed cargo lights but the two vertical bed lights in back are a mystery. Can anyone tell me what external switch is supposed to turn them on and where it is? I realize I can turn them on from the instrument panel cargo light switch. Please don't tell me that I need to open the truck if I'm already out to turn them on.

Sounds like you are having a similar problem to the OP. That switch in the bed is supposed to turn those lights on.
 
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