dash lights

[profbooty]

years back I installed vdo gauges, but used a common ground for the lights and for power which made the gauges give incorrect readings dependent on the dimmer position when you turned on the lights.

I changed the power ground from a brown/white wire to a brown wire which got rid of the strangeness if you turned on the dash lights. A few seconds later the dash lights went out. If i flip the dimmer to the first/second position the radio lights dim, but can not be adjusted. Lighting to the OBC, lighter and dash cut out. Sidemarkers, all the lights on the rear, hazards, etc are fine. AC switch doesn't light up at all (with parking lights on and off) hazard switch lights up, defroster lights up.


Fuse at pin 23 is fine, but i have no power at fuse 23's location. All the other lights on that fuse light up just fine. Any suggestions on where to start for troubleshooting? 1990 325is

[profbooty]

Any suggestions on troubleshooting the dimmer switch itself? I replaced it about 7 years back.

[profbooty]

Looks like pins 2 and 6 correspond to the pot. I'm getting .9 mili ohms resistance regardless of position. I'm guessing thats why my dash lights are out. Strangely my aftermarket head unit turns on illumination though.

Might jump pins 2 and six and see if that fixes it

[profbooty]

Solved.

I took apart the potentiometer inside of the dimmer switch. Couldn't get continuity between the coil and the output pin due to the coil having broken, despite not being visibly broken. a quick dab of solder fixed the issue and restored full dimming function.

https://imgur.com/4n9awqc documents steps similar to what I did to fix it, though my light switch looks a bit different. There's no need to solder between pins 2 and 6, just follow his steps to reconnect the tab with the coiled wire. It only takes 2 minutes to disassemble the switch so you should do it right rather than loose the dimmer functionality.

[george graves]

Hmmm. I'm not sure if this applies to your problem, but for future google searches...

A common mistake that is made is that people test for ground on a harness, and they inadvertently choose the cluster dimmer light wire. It will look like ground when off, but when you turn it on - that's when issues arise. It's a common trap. For something like gauges, always best to find a real ground. The radio harness has one that is decent for 99% of things. But you can't go wrong with finding a "real" ground. On e30's and most of these older BMW's, looks for a bunch of brown wires that all lead to a lug. That's your ground. (brown is BMW's code color for ground, with only a few exceptions)