Well, my daughter went to driver her "new" 1991 240 at night for the first time and discovered that the instrument cluster lights do not light up. I checked the dimmer operation and it had no effect.

I'm assuming this probably means (in order of likelihood) either:

1. Bad fuse
2. Dead bulbs
3. Bad dimmer switch

Am I on the right track?

If so, can anyone tell me which fuse controls the instrument cluster lights? (I did a search of the forums and found that the 740s use fuse#21, but not sure if the same applies to the 240).

Is the instrument cluster straightforward to remove in order to replace bulbs? How many bulbs are there and can someone provide a bulb number/part number?

How common is it for the dimmer switch to fail?

Am I missing anything?

Thanks!

-Brent

 

CHECK FUSE PANEL FOR BLOWN FUSES

JUST THE INSTRUMENT LIGHTS DON'T WORK?
WHAT ABOUT THE GAUGES?

As far as taking out the instrument cluster: 6 out of 10 in difficulty...LOTS OF LITTLE LIGHTS THERE....LOTS OF THEM...JUNK YARD STUFF OR ORDER ONLINE...FCPEURO.COM OR IPDUSA.COM

start by removing the dimmer switch **** and the light switch ****...just grab and pull
2) remove the cover surrounding both *****...pull out or use a flat head screwdriver
3) remove phillips head screw(s) holding left side of cluster frame
4) remove plastic square (a clock is here sometimes) on right side of cluster with a flat head screw driver
5) remove the phillips screws holding cluster frame...

MAKE SURE TIRES ARE STRAIGHT OR STEERING WHEEL EVEN....FOR ACCESS...
PULL OUT CLUSTER SLOWLY UNTIL IT HITS THE STEERING WHEEL OR A LITTLE BIT BEFORE IT HITS THE STEERING WHEEL.....
6) look on the right side and you will see the connections.....TAKE NOTE...three are simple to connect back...as they only belong to a certain connection...you might have to take extra note of the little connections....one or two for your car....

7) after taking all wires off...slide cluster to the right....there you go...

YOU CAN TAKE IT APART EASY...A FEW SCREWS ON THE EDGES AND MAYBE ONE OR TWO ON THE CENTER.....

THIS IS ASSUMING YOU DON'T HAVE ANY FUSES/RELAY BLOWN...

 

Thank you for the detailed explanation! The gauges seem to work (e.g. engine temp gauge registers and goes up and down depending on conditions).

I also noticed that the AC rocker switch, when switched on, does not light up - should it? If so, and it is on the same fuse as the dash lights, then it is looking more and more like a fuse...

 

I finally remember the name of the switch that controls the lights.......Rheostat

Looking at a instrument panel and light control circuit diagram...I remembered that this switch/fuse can screw up your lighting......

under steering column....and may look like the picture I included...not directly under steering column...you have to stick your head way back there where the pedals are attached all up in that area...

Rheostat controls the following:

Fasten Seat Belt light
Ashtray Light
Panel Lighting
Instrument lighting
clock
auto transmission gear selector light

 

OK, so I found a couple of bad fuses and replaced them, which fixed the problem with the central locking not working, but still no dash lights.

I have tried twisting the rheostat ("dimmer") switch all the way in both directions (at the end of one turn it seems to have a slight "click" - should this turn on the dome light?).

Speaking of dome light, the main dome light works, but only when it is manually switched on (in the far right position). Which position is supposed to come on with the doors? I tried both the middle and far left positions and neither activates with the doors. Could this be related to the dash lights?



Here is the dimmer switch, just for orientation:



Are any of these switches supposed to light up with the dash lights? (they aren't):




Trying to determine if this is a good learning opportunity for a father-daughter project, or if I should just take it to a shop to get it fixed.

it is however a convenient excuse for not letting my daughter drive at night...

 

the dome light middle position is off, so the opposite of always on is on-with-doors.

you can't use 740 wiring anything instructions with the 240, they are wired totally differently. my greenbook wiring diagram suggests its fuse 16, 8 amp, which is powered by the headlight switch...

the circuit goes... battery + to the 'positive terminal' (small black box full of red wires on left fender side of engine compartment) to fuses 7-10 (these are all circuits that are always powered) and to the headlight switch pin 30. when the lights are in parking or on, headliht switch pin 58 goes via a white wire to fuse 15 and 16.

fuse 16 has a green whire to the dashboard dimmer pin 58b. the dimmer pin 58a has a brown wire that goes to various places including the instrument lights, the clock light, and the panel switch lights.

the ashtray, and seat belt latches are powered by a red-white wire that comes off dimmer pin 58b (the input side of the dimmer).

so... turn headlights to the parking light position, take a volt meter, and see if there's voltage on fuse 16 relative to chassis ground. if there is, then the problem si downstream from there, probably around that dimmer switch.

btw, on any 240 with those dreaded 'euro' ceramic fuses, I *highly* recommend replacing ALL the fuses with new REAL european ceramic fuses that have brass or copper elements, these can be bought quite inexpensively off ebay as "Mercedes W123/W124 fuses", the various vendors sell a complete kit of these which are more than enough to do a 240 completely. the silver/tin/aluminum fuses sold here in Buss or other brand little hang cards at the parts stores are JUNK. take a clean pink pencil eraser to the inside of the fuse holder contacts to remove any oxidation around the little hole without stripping the gold plating, and replace ALL the fuses.

 

Thanks for the detailed explanation - just what I need to at least isolate the problem (though getting up under the dash to probe the pins on that dimmer switch is not going to be easy!) I tried climbing up under there yesterday and could barely reach up there to see a glimpse of the back of the dimmer switch..

I'll figure out where the problem originating and then report back.

 

verify there's power at the fuse first. thts easy, don't even need a volt meter, a 12V test lamp will do it, clip it to chassis ground, and touch the probe to fuse 16.

 

I have seen instrument clusters with burnt circuit boards that resulted in loss of all the lighting of the bulbs. If you verify power from the fuse and still have no luck, I'd recommend pulling a $30 instrument cluster from a junk yard and swapping them out. just make sure to do some research on which years instrument cluster will work with your 240, definitely stay away from the pre-86, as they have a cable driven speedometer vs the later style electronic speedometer.

 

ABS and non ABS is another difference. the ABS cars have more 'teeth' on the tune wheel in the rear axle, so the speedo divides down by a larger number.

 

Is there a way to access the dimmer switch without pulling the entire instrument cluster (per analogies' instructions above)?

 

not really. the switches are installed from behind the dash, the only way to get in there is through the instrument panel opening.

have you checked to see if there is power at fuse 16 when the ignition and headlights are on ?

the instrument and switch light circuit on fuse 16 is wired so its on when either the parking lights are on with or without the ignition, or when the headlights are on with the ignition on. to do this, it goes through some funny zigs in the headlight switch.

 

Pulling the instrument cluster is pretty straightforward and will need to be done anyway if you are to check the bulbs. All you need to do is remove the dash trim pieces just to the left and right of the instrument cluster. They just snap in. This exposes 4 screws that hold the cluster in. Remove the screws and slide the cluster towards you. Remove the wires attached. Mark each one - carefully. The cluster illumination bulbs can be removed from the back of the cluster. Check each one and replace as necessary.

When re-installing the cluster, if you have a red/white wire not connected to anything behind the cluster DO NOT FIND A HOME FOR IT. It is for the tachometer and if you don't have a tach, it does not attach to anything. Many folks connect it to the cluster and end up frying the cluster.

 

Pay attention to that warning act1292 gave you in the last paragraph. I made the mistake he is having you avoid.

One other thing, as far as instrument cluster removal goes--I generally remove that plastic cover off the top of the steering column. It requires is removed with two torx screws, but makes the whole thing much easier in my experience. Mine 240 is a 91 also... do you know if yours has ABS or no? The AC question... the AC light only comes on (I'm pretty sure) if the AC works. So if the AC doesn't work or isn't charged, you'll get no AC light. The lighting for those swtiches is in a little light-bar above the switches that shines down and lets you see them. (In theory)

 

SB245 did you ever get your dash lights on? Not sure if my problem is the same...see below...

When I turn on my headlights in my '92 240 wagon, the #16 fuse blows out and the dashboard lights and passenger-side parking lights go dark. I tried bypassing my red bulb failure relay as described by Dave Barton here
http://www.davebarton.com/pdf/bulbfailure86-93.pdf
and at first I thought I had met with success. My dashboard lights were on! BUT my low beams no longer worked. The low beams worked fine before.

I can hear the high/low beam step relay making a click as I switch on the high beams (which work) and back down to low. So I don't think it's that.

I've triple checked my wiring and connections to match up with the bypass schematic on Dave Barton schematic. I've reached out to him as well, maybe I'll hear back.

Any other help would be appreciated!

 

The problem is likely in your high/low step relay, and probably unrelated to your dash lights. The internals of the step relay can get bent up with heat and age, allowing either the high or low beams to work, but not the other. I'm sure others will come in if there are other/better thoughts.

 

zjinqui1k I think there's a good chance that you're right. My new best friend Dave Barton at davebarton.com has a test in mind that I want to perform that will let me know for sure. We'll see....

 

I had a similar problem with low beams not working (intermittently) on a 93 245. I used Dave Barton's wiring diagram and discovered that the wiring to the high/low relay in the engine bay was loose. Once I plugged it in firmly the problem was completely resolved.