Francishart

I have an issue with my 94 r129, all the backlight illumination for the binnacle, climate control, gear selector, and door controls have stopped working.

When the headlights are switched on only the cigarette lighter bulb turns on all the rest do not turn on.

I've checked the bulbs they are ok and work when tested, I've checked the bulb socket with a multimeter and shows zero voltage.

Looked through the fuses in the engine bay and all seem fine none blown.

Can anyone help?

Thanks
Francis

SRHsl600

Is the wiring harness been upgraded? If so, you must be able to drive the vehicle!
Have the fuses been converted to Cu instead of the Al ?
I would suspect the light switch system. So the multi plug fuse like thing under the driver knee pad is where I would look first.

Francishart

Thanks for the reply,
The car does drive fine but I'm unable to to see anything inside at night.

I don't think the hardness has been upgraded.
The bulk fuses are in the engine bay or trunk and use the cylinder style fuses (rather than blades).
I've taken out the light switch under the drives knee, inspected the loom and switch all looks good.

I've also noticed the cigarette lighter backlight turns on when the headlights are switched on so I'm fairly sure the light switch is functioning correctly.

As for a fuse under the drivers knee I've not been able to find this..?

F

SRHsl600

The space, above the driver footwell near the steering wheel has several connectors that control the light switch, turn signal, headlamp et al. I have paid to replace a relay for the turn signal, high beams years ago that was far beyond $$$ the relay of other cars! Since you have light switch function the problem is down the line. Look to a relay?

Francishart

so i finally sorted this out, after doing some reading on how this interior light circuit works it turns out that all but the cigar lighter bulb is dimmed and controlled via the rheostat in the instrument binnacle.

based on this i took apart the binnacle, and while the binnacle looked and tested fine. the PCB track feeding the rheostat however was not. it had burned through, a simple soldering repair and reassembly has now sorted it.

thanks for all the help