Interior light problem
Moderator: martauto
Hi all,
This is my first question on here and am hoping some one can help.
My interior light wont switch on if i open the drivers door but it will do if the passenger door is opened.
I checked the pin switch on the pillar and even bypassed it and still the same issue?
Any input will be appreciated.
This is my first question on here and am hoping some one can help.
My interior light wont switch on if i open the drivers door but it will do if the passenger door is opened.
I checked the pin switch on the pillar and even bypassed it and still the same issue?
Any input will be appreciated.
- Brianmoooore
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First thing to establish is whether you have the optional switch off delay module for the light fitted.
What are the exact colours of the wires connected to the two front door pin switches?
What are the exact colours of the wires connected to the two front door pin switches?
Also, the switch on the light itself has three positions, permanently on, permanently off, and switched from the door switch. Have you checked that the switch is in the correct position, does the light come on permanently when it should, and have you checked the unit, it is not a particularly robust item and easily broken?
The wire colours are brown/blue mix and a brown wire. Is there 2 relays one for each door or are they both connected to one relay?
@ChrisHC as started in my question above, the light will turn on if the passenger door open, so they are set in the correct possiton and working.
@ChrisHC as started in my question above, the light will turn on if the passenger door open, so they are set in the correct possiton and working.
- Brianmoooore
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Brown/blue is the wire to the switch that controls the relay that allows you open the windows with the engine off and a front door open.
The other wire is the one the controls the lights, but it is not plain brown, unless someone has been messing. It's colour should be brown/blue or brown/yellow.
There are no discrete relays involved with the operation of the interior lights.
The other wire is the one the controls the lights, but it is not plain brown, unless someone has been messing. It's colour should be brown/blue or brown/yellow.
There are no discrete relays involved with the operation of the interior lights.
- Brianmoooore
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If the wires to both switches are brown/purple and brown/blue, then you do not have a light delay module fitted. The wire to the driver's door switch would be brown/blue and brown/yellow if you had.
Unscrew and pull out the driver's door pin switch, disconnect the brown/purple and connect it to a good body earth or battery negative with a piece of wire. Do the interior lights come on?
Unscrew and pull out the driver's door pin switch, disconnect the brown/purple and connect it to a good body earth or battery negative with a piece of wire. Do the interior lights come on?
Switches can corrode and I have used these---just have to transfer the rubber cover.
https://www.ebay.co.uk/itm/UNIVERSAL-CA ... 0738636835
https://www.ebay.co.uk/itm/UNIVERSAL-CA ... 0738636835
- Brianmoooore
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OE switches are stainless steel and don't corrode. A small sliver of black plastic can build up where the contact surfaces meet however, but can easily be removed with a craft knife.
OE switches are double pole. These are only single.
Was there ever a solution to this? I have the identical problem.
All three of my other doors trigger the interior lights in their door-activated position. The driver's door does nothing.
What it DOES do, is light the electric window switches when you open the driver's door.
The wires are brown/blue and brown/purple. Brown blue is sitting at 12v. Brown purple is at 5v (odd?) Grounding the brown purple does nothing. I've also swapped the 2-pin switch for a brand new identical one from BMW.
I don't have a wiring diagram for this circuit so I can't really figure out what's going on. Am I right in thinking the other door pins simply break a circuit when they are pushed in, and when the door opens, they make the circuit?
The driver's door is obviously different with the 2 connectors. When the door is shut, the pin pushes in and disconnects the two wires from each other. When the door opens the body of the switch connects the two wires together.
The electric window illumination is somehow still working. What do I do next? Help!
All three of my other doors trigger the interior lights in their door-activated position. The driver's door does nothing.
What it DOES do, is light the electric window switches when you open the driver's door.
The wires are brown/blue and brown/purple. Brown blue is sitting at 12v. Brown purple is at 5v (odd?) Grounding the brown purple does nothing. I've also swapped the 2-pin switch for a brand new identical one from BMW.
I don't have a wiring diagram for this circuit so I can't really figure out what's going on. Am I right in thinking the other door pins simply break a circuit when they are pushed in, and when the door opens, they make the circuit?
The driver's door is obviously different with the 2 connectors. When the door is shut, the pin pushes in and disconnects the two wires from each other. When the door opens the body of the switch connects the two wires together.
The electric window illumination is somehow still working. What do I do next? Help!

- Brianmoooore
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Brianmoooore wrote: ↑Wed Mar 13, 2019 6:39 pmA small sliver of black plastic can build up where the contact surfaces meet however, but can easily be removed with a craft knife.
It’s a brand new switch?Brianmoooore wrote: ↑Sun Jan 16, 2022 7:09 pmBrianmoooore wrote: ↑Wed Mar 13, 2019 6:39 pmA small sliver of black plastic can build up where the contact surfaces meet however, but can easily be removed with a craft knife.
- Brianmoooore
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Brianmoooore wrote: ↑Fri Mar 08, 2019 8:01 pmUnscrew and pull out the driver's door pin switch, disconnect the brown/purple and connect it to a good body earth or battery negative with a piece of wire. Do the interior lights come on?
No. That’s what I tried already. Nothing happens at all. All I know is that with it installed in the door the window switches light when the door opens and nothing else happens.
With the switch pulled out of the door frame I have 12v on the brown blue wire and 5v on the brown purple wire.
The old switch acted this way and so does the new one. Any ideas?
With the switch pulled out of the door frame I have 12v on the brown blue wire and 5v on the brown purple wire.
The old switch acted this way and so does the new one. Any ideas?
- fixedwheelnut
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Brianmoooore wrote: ↑Sun Jan 16, 2022 8:05 pmBrianmoooore wrote: ↑Fri Mar 08, 2019 8:01 pmUnscrew and pull out the driver's door pin switch, disconnect the brown/purple and connect it to a good body earth or battery negative with a piece of wire. Do the interior lights come on?
Not too worried about the interior light fault but I would just like to say I am glad to see you posting again Brian, you had us all worried there for a while

- fixedwheelnut
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I would check the circuit from the lamp holder down to the switch, the fact you have 12v on the brown/blue wire with it off indicates there is continuity but there could be a high resistance somewhere so when current starts flowing it gets held up. Prime suspect is usually the lamp unit itself.silent32 wrote: ↑Sun Jan 16, 2022 8:28 pmNo. That’s what I tried already. Nothing happens at all. All I know is that with it installed in the door the window switches light when the door opens and nothing else happens.
With the switch pulled out of the door frame I have 12v on the brown blue wire and 5v on the brown purple wire.
The old switch acted this way and so does the new one. Any ideas?
I will check that as well thanks. They are also brand new Hella interior lights and bulbs too.
So just to be clear, the switch should ground both the electric window relay and the door-triggered interior light circuit when the door opens? Nothing more complicated than that?
So just to be clear, the switch should ground both the electric window relay and the door-triggered interior light circuit when the door opens? Nothing more complicated than that?
- fixedwheelnut
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exactly, probably the simplest part on the carsilent32 wrote: ↑Mon Jan 17, 2022 6:53 amI will check that as well thanks. They are also brand new Hella interior lights and bulbs too.
So just to be clear, the switch should ground both the electric window relay and the door-triggered interior light circuit when the door opens? Nothing more complicated than that?


Excellent, many thanks. Sorry if it’s a bit of a stupid question, I’ve just never had interior light problems in any car before!
I’ll do a continuity test and it should show up a resistance between the interior light itself and the brown/blue at the door switch. Presumably it runs pretty much direct from one to the other down a single wire?
I’ll do a continuity test and it should show up a resistance between the interior light itself and the brown/blue at the door switch. Presumably it runs pretty much direct from one to the other down a single wire?
The Master has returnedBrianmoooore wrote: ↑Sun Jan 16, 2022 7:09 pmBrianmoooore wrote: ↑Wed Mar 13, 2019 6:39 pmA small sliver of black plastic can build up where the contact surfaces meet however, but can easily be removed with a craft knife.

Mart.
Only the E46 cab left now.
Just got too old.
Just got too old.
The results are in:silent32 wrote: ↑Mon Jan 17, 2022 12:49 pmExcellent, many thanks. Sorry if it’s a bit of a stupid question, I’ve just never had interior light problems in any car before!
I’ll do a continuity test and it should show up a resistance between the interior light itself and the brown/blue at the door switch. Presumably it runs pretty much direct from one to the other down a single wire?
The body of the driver's door switch does ground when screwed in.
The brown/blue at the driver's side interior light is at 12v.
The brown/blue at the switch is also at 12v.
Resistance of 100 ohms between switch and light.
Can't remember much electrical theory. Assuming it's the same piece of wire running from the switch to the light, how do I get at it to find the dodgy bit? I'm used to wires that either break, or don't, not give 100 ohms of resistance? The terminals at both ends are good and solid. Any help, or further tests I can do appreciated.
- fixedwheelnut
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I take it you are measuring the resistance with the power off, the 12v will effect the ohm meter, pull the fuse for the interior lights and recheck it.silent32 wrote: ↑Tue Jan 18, 2022 2:57 pmThe results are in:silent32 wrote: ↑Mon Jan 17, 2022 12:49 pmExcellent, many thanks. Sorry if it’s a bit of a stupid question, I’ve just never had interior light problems in any car before!
I’ll do a continuity test and it should show up a resistance between the interior light itself and the brown/blue at the door switch. Presumably it runs pretty much direct from one to the other down a single wire?
The body of the driver's door switch does ground when screwed in.
The brown/blue at the driver's side interior light is at 12v.
The brown/blue at the switch is also at 12v.
Resistance of 100 ohms between switch and light.
Can't remember much electrical theory. Assuming it's the same piece of wire running from the switch to the light, how do I get at it to find the dodgy bit? I'm used to wires that either break, or don't, not give 100 ohms of resistance? The terminals at both ends are good and solid. Any help, or further tests I can do appreciated.
How are you doing brian!Brianmoooore wrote: ↑Sun Jan 16, 2022 8:05 pmBrianmoooore wrote: ↑Fri Mar 08, 2019 8:01 pmUnscrew and pull out the driver's door pin switch, disconnect the brown/purple and connect it to a good body earth or battery negative with a piece of wire. Do the interior lights come on?
Pulled fuse, now gives no continuity at all from switch to light and 12v at both brown/blue and brown/purple at the switch end. At the light end, nothing on the brown wire, weirdly 1.5v on the brown/purple.
Grounding the light works to illuminate it so at least that works. Now just a case of finding where the break is in the brown/purple wire. Previous owner had some work done on the sunroof, guessing the wire runs up the A-pillar, along the edge of the roof to the driver's side light? Any tips on how to get at it?
Grounding the light works to illuminate it so at least that works. Now just a case of finding where the break is in the brown/purple wire. Previous owner had some work done on the sunroof, guessing the wire runs up the A-pillar, along the edge of the roof to the driver's side light? Any tips on how to get at it?
- fixedwheelnut
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OK lets start fresh I have added notes to the diagram with the door shut so door pin switch is open no contact, you have 12 volts via fuse 21 up to the interior light bulb, because the brown purple wire is not earthed you will still measure 12 volts up to the switch.
With the door open the brown purple wire is connected to earth and current will flow through the bulb, so you will measure 12 volts up to the bulb and 0 volts - 0.5 volts on the brown/ purple wire.
Critical points for open circuit are the three pin connecters C303 and C304 at the base of each 'A' pillar and the position of the interior light switch itself which can be
1/ On all the time
2/ Off
3/ On when the door opens
Switch open door shut position and interior light switch switched to on with door open. Light will be off

Switch closed door open and interior light switch switched to on with door open. Light will be on.

With the door open the brown purple wire is connected to earth and current will flow through the bulb, so you will measure 12 volts up to the bulb and 0 volts - 0.5 volts on the brown/ purple wire.
Critical points for open circuit are the three pin connecters C303 and C304 at the base of each 'A' pillar and the position of the interior light switch itself which can be
1/ On all the time
2/ Off
3/ On when the door opens
Switch open door shut position and interior light switch switched to on with door open. Light will be off

Switch closed door open and interior light switch switched to on with door open. Light will be on.

That's really helpful, thanks for taking the time to sketch it all out. I don't think I'd really properly understood that the power is at the lamp but the switching is at the door. Everything at the lamp end is tested and fine, except no continuity between the brown purple at the lamp and the same wire at the door switch.
So the most likely break is down at the bottom of the A-pillar, as I know the door switch is fully working and so is the lamp - both are new, but I have tested all their contacts also just in case. Guessing the brown purple wire has a connection to both lights, but is it somewhere in the roof (I have a sunroof) or at some other earth distribution point?
I'll start digging around down there, and probably tackle my brake light switch while I'm in the footwell area, as my brake lights seem to be constantly on as well.
So the most likely break is down at the bottom of the A-pillar, as I know the door switch is fully working and so is the lamp - both are new, but I have tested all their contacts also just in case. Guessing the brown purple wire has a connection to both lights, but is it somewhere in the roof (I have a sunroof) or at some other earth distribution point?
I'll start digging around down there, and probably tackle my brake light switch while I'm in the footwell area, as my brake lights seem to be constantly on as well.
Have done my digging while changing the front speakers and tidying up under the dash. Brown purple from door switch disappears off into the loom and is not connected in any way to the interior lights. Another brown purple is hanging there with a spade terminal and this also comes from the loom and connects to nothing. Grounding the light itself works fine. So all I need to do is run a bypass wire from the light to the switch. What’s the easiest route?