Idiot Light On 87 300td - PeachParts Mercedes-Benz Forum

COLDSTART · #1 04-24-2007, 08:19 PM

the light that tells you that a bulb is burnt out is on all the time even when the light switch is off and all the lights are working fine any help thanks

300SD81 · #2 04-24-2007, 08:32 PM

I think you might be talking about the glow plug light or break pad light.. There is no bulb out light that I know of..

babymog · #3 04-24-2007, 08:40 PM

There is.

It doesn't work without the key on normally though.

C Sean Watts · #4 04-24-2007, 08:40 PM

Quote:

Originally Posted by 300SD81

I think you might be talking about the glow plug light or break pad light.. There is no bulb out light that I know of..

I think they come on when a ground is (from the burnt out bulb) is not carrying 'correct' current. Look for a corroded bulb socket or connector -BTW happy hunting.

300SD81 · #5 04-24-2007, 08:41 PM

Hmm, anyone have a pic of the light? I don't think I've ever seen it

Jeremy5848 · #6 04-24-2007, 08:44 PM

The "exterior light failure indicator lamp" on my '87 300DT is under the tach/clock, in between the windshield washer reservoir light and the ABS light. According to the owner's manual, if the indicator glows, it indicates a lamp failure. For headlights, etc., the indicator will come on when you try to switch the failed lamp on. For brake and turn signal lamps, the indicator will come on when you try to use that function and will stay on until the ignition is switched off. This suggests that there is an electronic circuit somewhere doing all this monitoring. Failure of the circuit might make the indicator lamp come on all the time. I'll do some research in the schematics, try to find this circuit, if it exists.

Jeremy

300SD81 · #7 04-24-2007, 08:56 PM

Quote:

Originally Posted by Jeremy5848

The "exterior light failure indicator lamp" on my '87 300DT is under the tach/clock, in between the windshield washer reservoir light and the ABS light. According to the owner's manual, if the indicator glows, it indicates a lamp failure. For headlights, etc., the indicator will come on when you try to switch the failed lamp on. For brake and turn signal lamps, the indicator will come on when you try to use that function and will stay on until the ignition is switched off. This suggests that there is an electronic circuit somewhere doing all this monitoring. Failure of the circuit might make the indicator lamp come on all the time. I'll do some research in the schematics, try to find this circuit, if it exists.

Jeremy

Ok.. That probably explains it, mines a 81, and most cars I've messed with at the junkyard were pre-85

Bio300TDTdriver · #8 04-24-2007, 10:12 PM

Quote:

Originally Posted by COLDSTART

the light that tells you that a bulb is burnt out is on all the time even when the light switch is off and all the lights are working fine any help thanks

Check the brake lights. I had one that was still working, but it set the light off.

Chris

Jeremy5848 · #9 04-24-2007, 10:30 PM

OK, there's something called N7, the "exterior lamp failure monitoring unit." In the schematic, it's just a "black box" with a transistor symbol on it (and, no doubt, a label saying "no user-serviceable parts inside"). It lives in F1, the Fuse/Relay Box, in "position K," at the rear of the fuse box. That's on the left (driver's) side, next to the firewall.

justinperkins · #10 04-25-2007, 12:15 AM

I love that little light, with it I am always instantly aware of a burnt bulb (or bad connection).

Before going any further, you need to make sure that all the bulbs are the correct wattage. If any of them are wrong (either high or low), the bulb warning system will be triggered. After all, it relies on a certain voltage draw when certain lights are on, therefore IT IS CRITICAL for the system to work properly that you have the correct bulbs.

Here are some steps to troubleshoot:
1) Turn key to on (not start), bulb warning lamp should be lit. If it's not, check the bulb warning module (described above)
2) Start engine, light should go off.
3) Right now you have no lights on. Don't put your foot on the brakes just yet. Is the warning lamp still off? I hope so.
4) Put your foot on the brake? Warning lamp on now? Check your brake light bulbs.
5) Turn on your parking lights. Warning lamp on now? Check your parking lights. Use the L/R parking light positions (to the left of center) to determine which side is burned out or has a bad connection.
6) Test the headlights, high beams and fog lights in the same manner.

From my experience, the front parking/turn signal lights are prone to having a bad connection. Also the fog light housing plastic is prone to cracking/breaking, which will cause the bulb to burn out. Lastly, the plastic that keeps the taillight bulb assembly in place is also prone to breaking. If it breaks, the bulb assembly will back out of the taillight housing and bounce around when you drive, causing bulbs to burn out.

Good luck.

JimFreeh · #11 04-25-2007, 08:07 AM

Looks like 3 relays end to end, and a black cover. Three groups of pin outs. You need to unscrew the cover behind the pop open fuse box cover to access this unit.

Euro versions are similar, but have one less pin in the middle group.

Jim

3pointstar · #12 04-25-2007, 07:38 PM

I had a 87 e300D turbo--- wonderful car. I too was troubled with the light that indicates that a bulb is burned out. IT DROVE ME NUTS. I checked every bulb in the car. My wife I think is perminently blinded in one eye from all the times I asked her to check the turn signals. Finally, I called MB and asked for help. The guy that I spoke with asked if I checked the light on the rear deck--- DID I FEEL STUPID-- Guess what light was out?? Yep --- the rear deck light.

COLDSTART · #13 04-25-2007, 08:26 PM

The light is on the whole time even if the lights are out, Volvo has a similar system which i have lots of experience with but I knew the Germans would do it differently that is why I asked thanks I will try your suggestions , the Car is from Texas spotlessly clean and only 147,000 miles .

justinperkins · #14 04-25-2007, 08:38 PM

Just to reiterate: Proper bulb wattage is CRITICAL to the bulb warning light system.

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