'84 300D Wierd light problem - PeachParts Mercedes-Benz Forum

Bruce Bonds · #1 03-23-2004, 10:18 PM

After replacing my daughter's alternator, I noticed that the instrument panel lights and the tag lights come on when the switch key is turned on. Normally, they come on only when you turn on the parking lights or headlights. This is not a problem except that I will have to replace bulbs more often. Anyone had a similar problem?

Fisherman · #2 03-24-2004, 01:22 PM

Could it be that somehow the connections got mixed up with the alternator warning light?
Obviously this idiot light comes on when you first turnt he key prior to starting. Sounds like somehow the dash lights got connected to this circuit.
Possible that the plug ont he back of the instrument panel got put back on incorrectly?

I'm just guessing but this is where I would start.

Bruce Bonds · #3 03-24-2004, 07:01 PM

Thinks for the quick reply, Fisherman. I'm not even sure it's related to the alternator replacement. The problem could have been there before. Today I noticed that the tiny side marker lights are coming on, along with the instrument panel and the tag lights when I turn the switch key. Maybe it's the light switch itself that is the problem. I jiggled it from position to position but no change. Oh well, I'll keep looking.

Bruce Bonds · #4 03-27-2004, 12:00 AM

Now I'm really confused. My p/s rear power window has never worked. I was messing with the window switch and the instrument lights went on and off. I kept pushing it and the instrument lights along with all the toggle switch lights and acc lights went out and are dead now. I changed the window switch (the front still works but not the rear) and still no dash lights. I changed the fuse too. However, now the tag lights are working properly as are the little side marker lights.

Do the instrument panel lights have any thing to do with the window switch?

Does the white rheostat behind the instrument panel also control the toggle switch lights for the sunroof/ant./ rear defrost/ rear int. light, and the lights on the acc panel? None of these light work now.

79-240d-project · #5 03-27-2004, 12:46 AM

Bruce,

I do not know if this will help but I just did some work on my instrument cluster. I had no dash lights or control panel lights. I replaced the dimmer switch(rheostat) in the instrument cluster and all dash and control panel lights now work just fine. I have a 240D with manual windows so I am not sure if a bad dimmer would cause issues with lighted switches on the doors.

Bruce Bonds · #6 03-27-2004, 07:42 AM

79-240D-project, thanks for the reply. I am going to either change or jump the rheostat. I'll let you know what happens.

I just can't figure out why the lights went out while I was working the window switch. Is there a connection here or just one of those strange coincidences that drive you crazy when you are trying to troubleshoot?

coachgeo · #7 03-27-2004, 09:19 AM

once I had a hot wire broke off and it would swing around and light things up when it found a ground etc.

Bruce Bonds · #8 03-27-2004, 06:39 PM

I just finished putting in a jumper wire to connect the two posts on the rheostat. Still no instrument panel lights, no toggle switch lights and no acc lights. Fuse checked OK again. The warning lights, glo-pug, seatbelt, etc. all work, as do the turn signal indicators.

Could I have a problem with grounding?

What should I check next?

Tirebiter · #9 03-28-2004, 02:16 AM

Just looking at a fuse will only verify that it isn't burned. Please take a test light and test both sides of the fuse holder. Often a fuse will not pass current because of slight corrosion. Just spinning a fuse in it's holder will sometimes correct the problem until you can clean the holder.

The mass of ground wires under the dash is also a place to check for loose bolts at the gang of ground terminals

Bruce Bonds · #10 03-28-2004, 06:04 AM

Tirebiter, thanks for the reply. I think I found the problem. I removed the instrument cluster (oil pressure, fuel, and temp) and found that the front side of the circuit board has broken places in the copper foil conductors. I'm going to replace the part and see what happens.

coachgeo · #11 03-28-2004, 08:17 AM

Quote:

Originally posted by Tirebiter
Just looking at a fuse will only verify that it isn't burned. Please take a test light and test both sides of the fuse holder. Often a fuse will not pass current because of slight corrosion. Just spinning a fuse in it's holder will sometimes correct the problem until you can clean the holder....

If that spot on your cluster does not solve the problem recheck the fuses. After rereading your combination of lights not working I too see that it could be a fuse. My unimog is the same way. I have one fuse that likes to blow and it takes out dash lights, "starter switch" ign. lights, and a few others.

Bruce Bonds · #12 03-28-2004, 05:02 PM

It's fixed. Thanks to all for the help. I replaced the cluster with the oil pressure, fuel, and temp guages. The front side is a circuit board. I found one at the junkyard for $4.60. I looked it over and all the circuits on the front side looked good. I know what to look for now. I can see that the inst. panel lights are working now and I can't wait 'til dark to see if the other switch lights are up again. Am I the only one that gets so much pleasure from a successful DIY fixit job? Maybe my posting all this will help someone else work through the same problem.

Fisherman · #13 03-29-2004, 09:47 AM

No you are not the only one, trust me in this.
How did you get the yard to part with just the oil pressure part of the cluster? My local yard wants 100.00 for the whole thing and won't seperate any of the parts. I have a bad fuel gauge and wanted to try to replace that part in the cluster and it was a no go when I asked them to sell me only that part.

Rick Miley · #14 03-29-2004, 02:02 PM

It depends on the yard. At some U-pull-it places, like the one here, you go in and get just the parts you need. Mine has even given away a few small parts when they didn't know what the parts was and hence didn't know what to charge.

Bruce Bonds · #15 03-29-2004, 03:53 PM

My local yard is a you-pull-it. I like the freedom there. For example, when I needed a bottom seat cushion, I just dismantled the seat in the yard, left the extra parts in the trunk of the donor car and paid $5.00 for the bottom cushion. As a matter of fact, I found the cluster above in a 300D trunk. Someone had carefully removed the speedo and left the other guages in place. I wish all yards were like this. I can practice and make all my mistakes at the yard and when I get home with the prize, I already know how to replace my part. Makes me look real smart and saves a lot of damage to my cars at home. I can't stand those yards that try to act like a parts store. Especially those that think that just because you are buying Mercedes parts that they charge a premium.