No interior illumination & number plate lights

[waj7d]

I've brought a Chrome Cab after almost 5 years away from anything e30 related and already ran into my first problem!

For some reason I have no interior illumination, when I turn on the headlights everything works externally ( apart from number plate lights), However internally only the electric windows buttons light up.

I have checked and double checked all fuses with no joy, I removed the headlight switch/interior dimmer and can confirm I have multiple 12v feed and the x2 earths (pin 2 and 6 I believe) are fine as these complete a circuit when checking with a multi meter.

I have also bridged pins 2 and 6 on the headlight switch/fader to bypass the dimmer with no joy.

I have also removed the speedo cluster and connected the bulbs directly to a battery and confirmed the bulbs are fine.

I'm not sure if the number plate issue is related, However the 12v feed is dead and again I have tested the bulbs..

Anyone have any ideas as I'm stumped and need to MOT the car ASAP to enjoy the last bit of sunshine we have left..hopefully..lol

[Brianmoooore]

Window buttons are powered from the window circuit itself, and should be lit all the time the ignition is on, or the front doors open.
The bulb illuminating the main lighting switch and the fog light switch should also be lit all the time the ignition is on.
The rest of the interior illumination and the number plate lights are powered from fuse 23, the same as the RH tail lamp and front parking light. You say these two exterior light are working, so fuse 23 must be OK, and feeding power to the lighting switch, on a grey/green wire.
The power is split internally to two different switch sections, and leaves the switch on a grey/white wire for the working tail and parking light, and on a grey/red wire for all the lights that aren't working.
Pull the plug off of the main lighting switch, and use a piece of wire to link together the grey/green and the grey/red wires. If this makes the non working lights come to life, then the switch is faulty. If it doesn't, follow the red/white wire and find the break.
The reason for this arrangement is so that the two RH parking lights can be left on (indicator switch), without all the rest of the bulbs providing an unnecessary drain on the battery.

[waj7d]

After tinkering around the light at dimmer is now on when you turn on the ignition, however it's not effected by the dimmer itself.

I have test by bridging the wires with no joy, how ever the red/grey wire (pin 1) and grey/white wire (pin 5) are both dead with of without the ignition.

Also I have tested the bulbs for the heater console and can confirm they are also Working

[Brianmoooore]

After tinkering around the light at dimmer is now on when you turn on the ignition, however it's not effected by the dimmer itself.

It shouldn't be. This bulb is not part of the main illumination circuit.

I have test by bridging the wires with no joy, how ever the red/grey wire (pin 1) and grey/white wire (pin 5) are both dead with of without the ignition.

Again, this is as it should be. The grey/green wire should be live, irrespective of which position the ignition switch is in, and both the grey/white and grey/red should be live with the lighting switch in the first and second positions.
You need to test to see if there is power on the red/white at the switch, with the switch on. This needs to be done with a 12 volt bulb, NOT a meter.

Also I have tested the bulbs for the heater console and can confirm they are also Working

[waj7d]

The grey/red is dead when the light switch is pulled into 1/2 position, however the grey/white is live when the light switch is puller into 1/2 position

I do not see a red/white wire.. Which pin should this be?

Oh by the way..thank you for the help so far..really appreciate it!

[Brianmoooore]

Sorry, red/white should read grey/red. The lighting switch needs to be on.

[waj7d]

Just tested with grey/red with light switch in position 1/2 with a bulb and I get nothing.

Grey/white is live when switch is in 1/2 position

[Brianmoooore]

Link the grey/red and grey/white wires together with a piece of wire and turn the lighting switch on.

[waj7d]

When bridging the wires together everything works! All interior lights, Dimmer and also the number plate lights.

Where does the grey/white go to from the headlight switch?

[Brianmoooore]

The power is split internally to two different switch sections, and leaves the switch on a grey/white wire for the working tail and parking light, and on a grey/red wire for all the lights that aren't working.

You have a duff lighting switch. Not a fault I have come across before, so I can't advise as to whether it can be opened up and repaired, or needs to be replaced.
Leaving the bridge wire in place as a temporary measure will be enough to stop you failing a MOT test on non working number plate lights, and a non illuminated speedometer.

[waj7d]

From my understanding its the dimmer that usually fails.. Well on a positive note I can put it in for an MOT tomorrow.

I'll keep my eyes peeled for another switch in the meantime. Thanks for all your help!

[Brianmoooore]

Failure of the dimmer section is fairly common, but usually only as a result of someone managing to short circuit the wires to one of the bulbs.

[capri_rob]

This is a prime example of what makes the E30 Zone great

Pretty sure the light switch is the same across all E30's so finding a used one at sensible money should be easy.