E39 dash lighting intermittent fault

[RoverP6B]

More electrical woes with my 540i... the latest thing is the instrument panel lighting dying! I think there must be a loose connection somewhere - the lighting to the dials (speedometer, tachometer etc) simply goes off. The dials themselves still work. Some of the centre console backlighting also dies. It's worth mentioning that the 540i also has by far the least effective rheostat of all my three E39s. Any thoughts?

[Huff]

Probably the rheostat itself - mechanical bits/moving contacts are usually the least-reliable elements in electronics.
If you can get at it, might be worth a squirt with contact cleaner to the innards while trying to source a replacement.

NB just a thought - given the amount of lighting it controls, and that patch of my dash never feels warm - it's probably a control potentiometer that then drives a mosfet or two hidden somewhere - i.e a low-power part, therefore a generic and susceptible to matching with the contents of the RS catalogue - if cheap bits from a scrapper not found.

[RoverP6B]

RS catalogue?

Is this going to be a dash-out job to fix? Bear in mind, I'm an owner-driver, not a mechanic or electronics specialist... I leave working on my cars to people who know what they're doing!

[Huff]

Probably not - I just stuck ' bmw e39 dash illumination adjuster' into Google image search - seems it is a little module pops out from the front

RS - eg. RS components, https://uk.rs-online.com/web/ : but the pics I find through doing the above,it's integration (you'll not find a commercial pot that small) and the low price for such BWM OEM parts on ebay, suggests its not worth trying that route. Good luck!

[anonymous-user]

RoverP6B said:

More electrical woes with my 540i... the latest thing is the instrument panel lighting dying! I think there must be a loose connection somewhere - the lighting to the dials (speedometer, tachometer etc) simply goes off. The dials themselves still work. Some of the centre console backlighting also dies. It's worth mentioning that the 540i also has by far the least effective rheostat of all my three E39s. Any thoughts?

Simple fix probably

[miniman]

Also worth noting that seemingly random electrical maladies are often also symptoms of a failing ignition switch. Mine suffered dash lights and wipers being intermittently borked.

[Hayek]

Is the battery in good shape? I got various electrical weirdness with a tired old battery, including the dash and headlights seemingly having a mind of their own at different times.

[RoverP6B]

Battery was new not long before I bought the car. Supposedly its predecessor was undersized. The radio gremlin is back, it dies intermittently. CD changer is totally dead, there's a magazine stuck in there too.