HELP!! License plate lights always ON, Witched 75 case?

Alexa · 19th January 2024, 10:02

I have a problem that is driving me crazy, the license plate lights are always on with the ignition and the switch lights in the off position, I have checked the voltage and I always get 12.7v to the positive wire of the license plate light, I have cleaned the ground connections, shiny as new, I have checked the cables that go from the trunk to the interior and everything is perfect, without corrosion, everything clean and shiny copper on the terminals.
The fuses are all checked and everything is fine.
I repeat, I always get 12v to the positive license plate cable with everything turned off at the controls.
Curiously, this problem happened to me when I removed the chrome bootlid from the trunk to polish and clean the paint in that area, and when I placed it and connected the license plate, the lights stayed on permanently.
The rest of the car works perfectly, everything turns off and on correctly, there are no short circuits or anything strange.
What I can do? Should I buy all new relays to rule out this option or does it have nothing to do with the problem?

I hope someone can help me, I would be eternally grateful

Mike Noc · 19th January 2024, 11:03

If it happened when you had the lights apart then check there aren't any extra wires put in by Mr Previous Owner - maybe for a live feed for a camera for example that you could have connected in place of the correct cable.
Failing that a battery disconnect costs nothing and is easy enough to do so worth a try. Only other things I can think of is a faulty Light Switch Module or faulty cabling between the LSM and the number plate lights where cables have rubbed through the insulation and you are picking up another live feed.

xsport · 19th January 2024, 19:13

Had a similar experience after a repair to my plinth.Lights going off and on whilst boot closed on the number plate.I found that the plinth seal had been compromised along the top edge letting in and retaining a volume of water in the lid itself. Why fuse did not blow , i have no idea !! Think you need to go back in there and check. I used some clear doublr sided tape ,trimmed to suit before re attatching the plinth, then all was good.However your problem may be from a different source , but you need to start somewhere ...

Mike Noc · 20th January 2024, 09:31

The fuse didn't blow because that circuit isn't fuse protected.

SD1too · 20th January 2024, 10:08

Quote:

Originally Posted by Mike Noc

The fuse didn't blow because that circuit isn't fuse protected.

To add to Mike's helpful post, none of the lamp circuits uses a conventional fuse except the front fog lamps and reversing lamps on cars with automatic transmission.

Instead short circuit protection is provided within the LSM by FETs (Field Effect Transistors) which are self-resetting once the fault has been rectified (source: RAVE).

Simon

Alexa · 26th January 2024, 10:20

Problem solved, there were two SMD capacitors burned in the LSM, I bought one from a scrapyard 75 and it is now solved, I just have to set it to TOAF. At first I had an error in the box, which is normal, but now the error has disappeared on its own, I will still check that it is linked correctly with the other modules.
The license plate light has symptoms of some water having entered, I have disassembled it, converted it to LED and sealed it completely for safety.

Mike Noc, xsport & SD1too, thanks you very much for trying to help me!

19th January 2024, 10:02	#1
Alexa Newbie Rover 75 Join Date: Sep 2023 Location: Madrid Posts: 13 Thanks: 0 Thanked 0 Times in 0 Posts	HELP!! License plate lights always ON, Witched 75 case? I have a problem that is driving me crazy, the license plate lights are always on with the ignition and the switch lights in the off position, I have checked the voltage and I always get 12.7v to the positive wire of the license plate light, I have cleaned the ground connections, shiny as new, I have checked the cables that go from the trunk to the interior and everything is perfect, without corrosion, everything clean and shiny copper on the terminals. The fuses are all checked and everything is fine. I repeat, I always get 12v to the positive license plate cable with everything turned off at the controls. Curiously, this problem happened to me when I removed the chrome bootlid from the trunk to polish and clean the paint in that area, and when I placed it and connected the license plate, the lights stayed on permanently. The rest of the car works perfectly, everything turns off and on correctly, there are no short circuits or anything strange. What I can do? Should I buy all new relays to rule out this option or does it have nothing to do with the problem? I hope someone can help me, I would be eternally grateful

19th January 2024, 11:03	#2
Mike Noc This is my second home Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4. Join Date: Jul 2009 Location: Hampshire Posts: 11,557 Thanks: 3,470 Thanked 3,119 Times in 2,247 Posts	If it happened when you had the lights apart then check there aren't any extra wires put in by Mr Previous Owner - maybe for a live feed for a camera for example that you could have connected in place of the correct cable. Failing that a battery disconnect costs nothing and is easy enough to do so worth a try. Only other things I can think of is a faulty Light Switch Module or faulty cabling between the LSM and the number plate lights where cables have rubbed through the insulation and you are picking up another live feed.

19th January 2024, 19:13	#3
xsport Posted a thing or two rover 75 club se Join Date: Apr 2011 Location: Leicester Posts: 1,673 Thanks: 358 Thanked 419 Times in 310 Posts	Had a similar experience after a repair to my plinth.Lights going off and on whilst boot closed on the number plate.I found that the plinth seal had been compromised along the top edge letting in and retaining a volume of water in the lid itself. Why fuse did not blow , i have no idea !! Think you need to go back in there and check. I used some clear doublr sided tape ,trimmed to suit before re attatching the plinth, then all was good.However your problem may be from a different source , but you need to start somewhere ...

20th January 2024, 09:31	#4
Mike Noc This is my second home Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4. Join Date: Jul 2009 Location: Hampshire Posts: 11,557 Thanks: 3,470 Thanked 3,119 Times in 2,247 Posts	The fuse didn't blow because that circuit isn't fuse protected.

26th January 2024, 10:20	#6
Alexa Newbie Rover 75 Join Date: Sep 2023 Location: Madrid Posts: 13 Thanks: 0 Thanked 0 Times in 0 Posts	Problem solved, there were two SMD capacitors burned in the LSM, I bought one from a scrapyard 75 and it is now solved, I just have to set it to TOAF. At first I had an error in the box, which is normal, but now the error has disappeared on its own, I will still check that it is linked correctly with the other modules. The license plate light has symptoms of some water having entered, I have disassembled it, converted it to LED and sealed it completely for safety. Mike Noc, xsport & SD1too, thanks you very much for trying to help me!