OBC back light

[Bonymaenjack]

Afternoon , my 13 button OBC has suddenly lost its display screen visibility ,its still fully functioning but is acting as if the bulbs have blown.
I have another car with an OBC in which is as it should be so I swopped the unit over but the same effect, I then put the original "faulty" one into my other car and its working fine , I've swopped the light bars over and both are fine .So I'm guessing something in the car is causing the problem and not the OBC itself . Can any one help.
Thanks in advance

[Speedtouch]

I presume you know about the dashboard lighting dimmer built into the headlights switch?

[Bonymaenjack]

I presume you know about the dashboard lighting dimmer built into the headlights switch?

Yes I’ve tried that ,I can’t remember the correct term for the operation ”aretrostat ? Of the dial but it looks like the loom and not the unit

[BenHar]

http://www.e30zone.net/e30zonewiki/inde ... d_Computer

Ben

[Bonymaenjack]

http://www.e30zone.net/e30zonewiki/inde ... d_Computer

Ben

Cheers Ben . yes I've read that , it maybe the light switch itself has failed as I have no instrument panel lights working at the moment

[Brianmoooore]

Check the number plate lights.

[Bonymaenjack]

Check the number plate lights.

Brian both are working as are all the others front and rear but no instrument lights for the gauges and the heater panel etc

[Brianmoooore]

Number plate lights are on exactly the same circuit as the instrument lights - all on grey/red wire and all are not required as 'parking lights'.
If the number plate lights are lit, and the instrument lights aren't, the most likely thing to be wrong is the rotary dimmer built into the main lighting switch.
Easiest test is to pull out the rear ashtray light and connect the brown/white wire directly to a good body earth ( e.g. handbrake securing bolt), which bypasses the dimmer.

[Bonymaenjack]

It’s definitely an earth fault ca using the non display of instrument lights but I’ve also noticed the dimmer isn’t working (the cars’ been off the road for 11 years so it’s now being recommissioned) can this be linked to the instrument earth fault also which earth point is the one used for the lights ?
Thank you

[Brianmoooore]

Earthing points on an E30 are on the LH inner front wing, low down at the front, a stud behind the centre of the glovebox, which sometimes has a second stud bolted to it, and a stud on the LH side of the rear seat pan, plus the terminal on top of the RH front suspension turret, where the battery and engine loom are earthed.
The rotary dimmer is connected into the earth path for the panel lights, so if it's open circuit, then none will light. Have you tried earthing the brown/white at the rear ashtray?
Also try connecting a 12 volt lamp between any of the grey/red wires behind the dashboard and earth with the lights on. There's one in the radio loom (which is often involved in the cause of a blown rotary dimmer.)

[Bonymaenjack]

Earthing points on an E30 are on the LH inner front wing, low down at the front, a stud behind the centre of the glovebox, which sometimes has a second stud bolted to it, and a stud on the LH side of the rear seat pan, plus the terminal on top of the RH front suspension turret, where the battery and engine loom are earthed.
The rotary dimmer is connected into the earth path for the panel lights, so if it's open circuit, then none will light. Have you tried earthing the brown/white at the rear ashtray?
Also try connecting a 12 volt lamp between any of the grey/red wires behind the dashboard and earth with the lights on. There's one in the radio loom (which is often involved in the cause of a blown rotary dimmer.)

Thanks Brian, yes I've tried as you suggested connecting the brown/white at the rear ashtray , that's when the instrument light up the off again when I remove it.I'll clean up all the earth points tomorrow and see what happens .Corrosion could have formed on an earth especially when the car has been become damp due to lack of use.

[Brianmoooore]

The dimmer earths at the point behind the glovebox, which isn't usually affected by damp.
If the panel lights come on when you earth the brown/white at the ashtray, then it's almost certain that the dimmer has failed.

[Bonymaenjack]

The dimmer earths at the point behind the glovebox, which isn't usually affected by damp.
If the panel lights come on when you earth the brown/white at the ashtray, then it's almost certain that the dimmer has failed.

I believe the car was stripped of its interior during the lay up so there was no soft material such as a carpet to absorb any moisture ,hence my reference to damp . Cheers

[Bonymaenjack]

Just a quick update, replacing the headlight switch solved the problem
Thanks Brian