Okay - dash lights possessed! - PeachParts Mercedes-Benz Forum

supersano · #1 11-29-2005, 02:43 AM

Here's my first post, but this forum has been a big help so far with my car - sorely neglected and slowly coming back to life.

Okay - the answer to this might be as simple as a pinched wire or a reversed plug somewhere, and I've checked all the dash light posts...anyway, this will be fun to explain. Okay - found a new used rheostat for my 73 280SEL. It starts out normal - before messing with it, everything on the interor worked fine, except gauges (speedo, clock, fuel/temp) and heater controls, and all exteriors worked fine. I tried turning it back and forth for a few hours until the little chrome nub chewed my fingertip off. After messing with: it likes to blow the #7 fuse and when it isn't blowing fuses, the gauge lights are on even when the car, electrics and headlights are turned off. Then, just for kicks, when I turn the headlights on, they turn off. Same thing with the dimmer unit completely removed.

Now - the fun part - it works better with the #1 fuse removed. Gauge lights are off at all times now; exterior parking lights are back on, but right (f and r) turn indicators flash at double speed while the blue brights indicator flashes on the dash; brights work when stalk is pushed in (locked), but when pulled back (toggle) all gauge lights turn on but the brights do not; low fuel and red "power" warning lights are on at all times; turn indicator and bright indicators also. I was having fun for a while flicking the bright stalk back and forth, watching the gauge lights and glove box alternately turn on and off. Probably all moot since I should have that fuse in, but then shouldn't all that just be off?

The heater lights never worked and still don't...I'll worry about them later...probably bulbs. I then cleaned and replaced the original dimmer - same thing with that one in. What did I do? My dad suggested I put a coin in the fuse holder and watch for where the smoke comes from. I'm about to, I tell ya. Thanks if you read this far.

250 Coupe · #2 11-29-2005, 06:59 PM

You've a bad or missing ground somewhere in the dash would be my guess. You can unleash some pretty gnarly gremlens just by lifting a ground.

Michael

supersano · #3 11-30-2005, 12:46 AM

Yeah, I've been contorting myself into nasty and unspeakable shapes trying to see under the dash for any loose or frayed wires but haven't found any yet. Tried banging around the interior trying to jar something, and hitting my steering wheel made my gauge lights come on for a bit, so it sure sounds like something loose somewhere. I'll keep looking. I love fixing these things...hitting computers just doesn't do anything anymore. Nothing good anyway.

300SDog · #4 11-30-2005, 05:43 AM

Like 250Coupe said, installing some extra grounding wires might help. Try hooking up a heavy guage wire from instrument cluster housing, say from one of the 7or8mm instrument attachment nuts to something on the firewall. And in the engine compartment you can hook up a massive braided grounding strap from engine to firewall, say from a bell housing bolt to something that attaches to sheet metal. Sometimes there's one there already. Also hosing electrics with WD-40 can help. And so can unplugging and reattaching electrical connections.

The best remedy I've heard for curing 19th century technology of the instrument light switch is to bypass it entirely. That dimmer switch is an inside joke among MB owners, easily the most primitive component on the car. Earlier ones are white porcelain and brass, very impressive looking and resemble something you might see at the Thomas Edison electrics museum.

meltedpanda · #5 11-30-2005, 08:32 AM

Quote:

Originally Posted by 240DieselDog

The best remedy I've heard for curing 19th century technology of the instrument light switch is to bypass it entirely. That dimmer switch is an inside joke among MB owners, easily the most primitive component on the car. Earlier ones are white porcelain and brass, very impressive looking and resemble something you might see at the Thomas Edison electrics museum.

I have my dash out and my dimmer switch was green, corroded and looked very bad. A few minutes with some 600 grit and contact cleaner and it looked like new, don't know if it works yet, and may be some time before I do, but it does look good

I celebrate small victories

300SDog · #6 11-30-2005, 09:44 AM

No small victory there if it works 100%, never in my life seen one fully functional.

boneheaddoctor · #7 11-30-2005, 09:56 AM

Quote:

Originally Posted by 240DieselDog

No small victory there if it works 100%, never in my life seen one fully functional.

Yeah..those dimmers vary the light from between dim to total darkness....few here will ever argue the dash lights are too bright. My eyes are light sensitive and I have excellent night vision and never find them too bright on ANY car I have ever owned.

supersano · #8 11-30-2005, 12:59 PM

Yeah, I tried bypassing the dimmer switch yesterday, but it makes no difference if there's either of 2 well-cleaned switches installed or it's bypassed. With all fuses in, the gauge lights want to stay on at all times, and at full brightness, which is actually pretty bright. It will blow any size fuse I put in #7, so I'm running around with both #1 and #7 fuses removed and things are lit that shouldn't be. Like the gauges for instance. No smoke or sparks, no dim or flickering lights - but the dimmer switch was pretty hot when I removed it again. I'm wearing a nice shirt today so I can't do it while I'm at work, but I'll try your suggestions and ground everything in sight.

300SDog · #9 11-30-2005, 01:05 PM

Quote:

Originally Posted by boneheaddoctor

I have excellent night vision and never find them too bright on ANY car I have ever owned.

Me too because MB's is all I've ever owned. But the worst I've seen is girlfriend's Toyota where dashlights would actually reflect and cast an image on the widshield glass at night.

boneheaddoctor · #10 11-30-2005, 01:55 PM

Quote:

Originally Posted by 240DieselDog

Me too because MB's is all I've ever owned. But the worst I've seen is girlfriend's Toyota where dashlights would actually reflect and cast an image on the widshield glass at night.

never owned a toyota...but I figure someone built one that needs a dimmer switch...

Tomguy · #11 11-30-2005, 05:59 PM

Well, my 108's dash lights are more than adequate for me. All but 1 of them work (that one is where the board cracked on me - oops!). The dimmer switch works, too. It took me a while to figure out how to do it - some epoxy to hold that coil inside its tracks. Once it's held there, it doesn't pop out and it actually works quite well.

supersano · #12 11-30-2005, 08:41 PM

Interesting - so your little coil was actually popping out? On both of the ones I have, it's pretty well jammed in there. More fun today - as I reversed and then put the shifter in park, the gauge lights came on - with no #1 or #7 fuse. Same thing happened last night, like it's a secret transmission code to get my IP lights on. Even when I'm exasperated I still have to laugh.

250 Coupe · #13 12-01-2005, 11:27 AM

It really doesn't have much to do with your troubles but here is a story about my brothers R15 (Renault 15 for those not in the know

)

He found one day that if the parking lights were on and he kept his foot on the brake pedal that the engine would keep running when he took the key out of the ignition.

He had great fun messing with passengers until we replaced the passenger side brake lamp. It was a cool smoked grey white inside and I assume was shorted from the brake filament to the parking filament.

Michael

Oh yah, wait till you lose the correct ground and all of your gauges pulse in time with the turn signals.

meltedpanda · #14 12-02-2005, 09:43 AM

I took my little ceramic coil apart, cleaned all surfaces of the green crap, sprung the springs a little and in a tedious process returned them back to the original configuration. Put it back in the dash and it works fine now. Dims and brightens all the lamps. I did jumper the two connectors prior to return to make sure the board was Ok.