Strange lighting problem - PeachParts Mercedes-Benz Forum

drbrandini · #1 02-18-2004, 08:36 PM

My front left running light and my tail light l/r are inop. However both have good bulbs. Fuse no. 8 runs them both however it is good also. Where should I go from here??

BTW: this is my 300E

Thanks for your help!

Gilly · #2 02-18-2004, 09:05 PM

How did you test the fuse? You may want to consider slipping in a new one, sometimes it's hard to find a fault with the fuse but there will be corrosion on the part where it engages into the fusebox.
Do you have a voltmeter to test to see if there is power to the bulb socket?
It could be a bad exterior lamp failure monitor control unit.

Gilly

drbrandini · #3 02-21-2004, 08:40 PM

Hey gilly,

Thanks for the response. I tried another fuse with no luck. I do not own a voltmeter, but now I have a good exuse to buy one. Thanks for the help!

Gilly · #4 02-21-2004, 09:10 PM

Hey, real simple one:
Possibly just the bulbs?
On the taillight, is the small one on the "side" of the tailight working, or are both the actual taillight and the rear sidemarker out too? Wouldn't hurt to check the bulbs, stranger things have happened.
Also curious, are you getting the bulb failure warning on the dash?

If you can't come up with a solution I can check over the wiring schematic. One possiblity is a control unit called the "exterior lamp monitor or exterior lamp control unit " (I think that's the official name for it).
It's in the fusebox, and as the name implies it monitors the current draw of all the exterior lamps (except possibly the headlights), and if the current draw is too high or low (usually low) it illuminates the warning light on the dash. It can do this because it provides the power to all of the exterior bulbs, so it's "easy" for it to monitor this. If I'm not mistaken it also acts as the "flasher" for the turn signals and 4 way flashers.
I've also seen problems in regards to the screws that hold the different wires to the bus strips on the underside of the fusebox. They can loosen up over time and cause problems like this. Checking something like this is where a voltmeter or maybe even a testlight can help alot.

Gilly

drbrandini · #5 02-23-2004, 10:01 PM

Hey gilly!

I tried the new bulbs and the fuse before my initial post with no luck. However, yesterday I had a chance to pull off the tail light and clean the grounding strips inside. Unfortunately with no luck again. My light is illuminated on the dash and you are correct it is only the running light on the drivers side rear and the drivers side corner running light (the blinker still works). I also pulled off the cover behind the fusebox, I don't really know what I'm looking for though. The two fuses in there were fine.

I do own a test light! What should I check?

Gilly · #6 02-24-2004, 05:16 AM

I'll look at a schematic tonight. So what is inop is: left front parking light (left front signal is OK) and what is inop in the rear? The left tail light itself, or is the left rear side marker also inop? You should have 4 bulbs working in the rear with the headlight switch on, the 2 actual rear-facing tail lights, and the 2 rear side markers (not including the license lamps here) along the side of the tail light lense. We have to find out for sure if the power is what the problem is, and I can help you do that. If that's OK, then we need to test the grounds. It seems more likely that it's a power supply problem, because it uses seperate grounds, but the power is all coming from the failure monitor.

Gilly

Gilly · #7 02-24-2004, 09:16 PM

The wiring is as follows:
From the switch, the signal for the left side runs through Fuse 8.
After the fuse the signal runs to what is called N7, which is officially called the Exterior Lamp Failure Monitoring Unit.
This seperates the signal out to the individual bulbs. Here's the wires you should check, just start at the lights themselves:
On the rear, on the connector that plugs into the bulb plate, the actual "tail/parking lamp is either socket 5 or 6 (lousy scans) and is a gray wire with a black stripe.
On the left rear side marker it's socket #1, white wire with a green stripe.
On the front left parking light, remove the light assembly, and on the connector for the socket, the parking light is socket 4, gray wire with a black stripe.

If the inop ones check out to have no power, then the course of action I usually took is to identify which socket is supposed to be providing power to the affected wires, and I would jump power to the individual socket from off the battery and see if the bulb would work OK then, if it did it means the module is bad. If it doesn't you have a wiring problem.

Gilly

drbrandini · #8 02-25-2004, 01:23 PM

Gilly,

Thanks a bunch for getting that info for me, that helps a bunch.
Sorry my post was confusing, the lights out are: drivers side corner running light and drivers side tail light running (the one on the back not the side marker).

Thanks

I will test those with my test light and let you know what I find.

drbrandini · #9 03-06-2004, 11:50 PM

Gilly,

We Finally had nice weather today so I got around to checking my lighting situation. I don't have power at the fuse box or the lights themselves. Any Ideas? Could it be my switch?

Gilly · #10 03-07-2004, 06:22 AM

If there is no power to fuse 8 with the parking lights or headlights turned on, I would tend to think it's the switch or a wiring problem, yes.

Gilly

drbrandini · #11 03-07-2004, 09:10 AM

should I try jumping power to the fuse box from the battery?

Thanks again for all your help!

Gilly · #12 03-07-2004, 03:54 PM

I don't think any harm would be caused if you try that.

Gilly

Hans47 · #13 01-07-2006, 03:01 PM

Hi, what was the solution to this problem? The driver side left side marker lamp on my 420 SEL burned out. I bought a replacement bulb at the dealership but it did not solve the problem. All of the other rear lights work (turn signal, stop, parking/standing and backup lamps). A warning inidcator lamp is not lit on the dash. This is very strange.

Hans47 · #14 01-07-2006, 03:16 PM

In my last post I forgot to mention that when I removed the existing bulb it was a 21W bulb and the filament appears to be intact. According the manual the side marker lamp should be a 10W bulb. Did this cause the problem?

Jakob F Prasz · #15 01-07-2006, 03:32 PM

Try to check the groundwires. Do you get a bulb warning? Have you checked the light control unit? Its located just above the fusebox.