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Roof lights won't turn off

Looks like something else was melting it, or rubbed through causing the short and subsequent melting. Was it touching exhaust or a sharp edge on something?
 
I have same problem, clearance lights won’t turn off. I pulled F 79 fuse to turn off. Dumb question but what’s best way to clean the connectors, wire brush, Sand paper , other?
Truck is 2022 3500 Limited
 
Jimmy07 said:
Ahhh, you’re the bumper fire truck…I’d say the running light circuit fried the trailer running lights relay control on the fuse box PCB, and the relay is stuck on 87, constantly feeding the cab lights
Click to expand...
I am having the same problem, how do I know which relay it is ? are they interchangeable ? Dealer has no clue...but will gladly charge me 149,95 an hour to try and figure it out...
 
Northman said:
I am having the same problem, how do I know which relay it is ? are they interchangeable ? Dealer has no clue...but will gladly charge me 149,95 an hour to try and figure it out...
Click to expand...
Clean your 7 pin plug
 
Too the plug apart no corrosion, all wiring around bumper is ok, nothing is pinched
 
Northman said:
Too the plug apart no corrosion, all wiring around bumper is ok, nothing is pinched
Click to expand...

Do you have the goose neck prep with the 7 pin in the bed? Perhaps it could be a faulty relay you could pull it and test it
 
H3LZSN1P3R said:
Do you have the goose neck prep with the 7 pin in the bed? Perhaps it could be a faulty relay you could pull it and test it
Click to expand...
I do not have the goose neck prep, I pulled out all the relays and the cab lights stayed on, the info in the fuse box is limited...
 
Northman said:
I do not have the goose neck prep, I pulled out all the relays and the cab lights stayed on, the info in the fuse box is limited...
Click to expand...
Pull fuse F79 and the clearance lights should go out. The relay @Jimmy07 was talking about is on the circuit board in the PDC, not one that is visible under the lid. The challenge will be to figure out if the relay is stuck or the BCM has erroneously made the ground for the relay. Back probing the green/white wire for 12 vdc on a voltmeter, either under the PDC or at the BCM might be the easiest route. If you have 12v the relay is stuck. If not it’s the erroneous BCM ground, and we’ll have to figure why that is. I guess another way would be to put the fuse in, find the green/white wire and cut it. If the lights go out the relay is not stuck and the ground is being applied to actuate the relay.
 
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PRS said:
Pull fuse F79 and the clearance lights should go out. The relay @Jimmy07[/US
[QUOTE="PRS, post: 285842, member: 143"]
Pull fuse F79 and the clearance lights should go out. The relay [USER=2576]@Jimmy07 was talking about is on the circuit board in the PDC, not one that is visible under the lid. The challenge will be to figure out if the relay is stuck or the BCM has erroneously made the ground for the relay. Back probing the green/white wire for 12 vdc on a voltmeter, either under the PDC or at the BCM might be the easiest route. If you have 12v the relay is stuck. If not it’s the erroneous BCM ground, and we’ll have to figure why that is. I guess another way would be to put the fuse in, find the green/white wire and cut it. If the lights go out the relay is not stuck and the ground is being applied to actuate the relay.
Click to expand...
I am a semi retired carpenter... not very knowledgable with automotive electrical... so first question ...PDC ? Power distribution center ? I Did pull fuse 79 and the clearance lights are off.
[/QUOTE]
BCM ? what is that and where is it located ?
PRS said:
ER] was talking about is on the circuit board in the PDC, not one that is visible under the lid. The challenge will be to figure out if the relay is stuck or the BCM has erroneously made the ground for the relay. Back probing the green/white wire for 12 vdc on a voltmeter, either under the PDC or at the BCM might be the easiest route. If you have 12v the relay is stuck. If not it’s the erroneous BCM ground, and we’ll have to figure why that is. I guess another way would be to put the fuse in, find the green/white wire and cut it. If the lights go out the relay is not stuck and the ground is being applied to actuate the relay.
Click to expand...
 
Northman said:
I am a semi retired carpenter... not very knowledgable with automotive electrical... so first question ...PDC ? Power distribution center ? I Did pull fuse 79 and the clearance lights are off.
Click to expand...
BCM ? what is that and where is it located ?
[/QUOTE]
Yes, PDC is the power distribution center.
BCM is the Body Control Module. Controls lots of the functions that reside as systems in the body of the vehicle. As in this case, the BCM controls the external lights. When lighting is requested, either through the manual on selection of the switch, or the automatic light sensor system, the BCM controls voltage to the various circuits to turn on the lights. Also in this case the clearance lights get their voltage via a relay in the PDC which is hot on one side all the time, but the relay is open until the BCM receives the signal to turn on the lights. At which time it provides a ground to the coil of the relay, the relay closes and voltage is supplied to the light circuit.
if the relay is stuck closed, the lights are on always. If there is a ground on the relay coil when there’s not supposed to be, the lights will be on. If you remove the ground and the lights go off, the relay is ok and you need to find why the ground is there when it’s not supposed to be.

The BCM is located behind the kick panel at the left end of the dash on my 2020.

What year is your truck?
 
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PRS said:
BCM ? what is that and where is it located ?
Click to expand...
Yes, PDC is the power distribution center.
BCM is the Body Control Module. Controls lots of the functions that reside as systems in the body of the vehicle. As in this case, the BCM controls the external lights. When lighting is requested, either through the manual on selection of the switch, or the automatic light sensor system, the BCM controls voltage to the various circuits to turn on the lights. Also in this case the clearance lights get their voltage via a relay in the PDC which is hot on one side all the time, but the relay is open until the BCM receives the signal to turn on the lights. At which time it provides a ground to the coil of the relay, the relay closes and voltage is supplied to the light circuit.
if the relay is stuck closed, the lights are on always. If there is a ground on the relay coil when there’s not supposed to be, the lights will be on. If you remove the ground and the lights go off, the relay is ok and you need to find why the ground is there when it’s not supposed to be.

The BCM is located behind the kick panel at the left end of the dash on my 2020.

What year is your truck?
[/QUOTE]
Thank you for all that info !

So basically this is above my pay grade... all those wires ... I guess I will be a t the mercy of the dealership...

I miss my 1976 mustang.
 
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