1987 300TD Headlight Wire Issues - PeachParts Mercedes-Benz Forum

frankstallone · #1 12-28-2008, 09:04 AM

So finally my driver side low beam decided to kick the bucket but not how you would normally expect. I replaced the headlights with aftermarket headlights that look like the later 320E's that were produced in 1995 which used the same harness as the tail lights if I am not mistaken. Anyway long story short I ended up testing and finding out the low beam headlight wire was causing a bad connection from the fuse box (fuse 13) to the headlight, causing the headlight not to work on the driver side only.
I tested a slightly larger wire from fuse 13 to the low beam peg on the headlight assembly and sure enough the low beam light came on instantly. Pleased with the test, I screwed the this slightly larger gauge wire into the wiring harness, out one of the rubber nipples conveniently there, strung it down the driver side of the engine bay and into the headlight wiring harness soldering the hallow peg to the end of the wire.
Turn the headlights on and smiled happily at a job well done. Later that night I get back into the car to return the H4 headlights I bought from Pepboys when I realize that when I turn my switch to the headlight position the indicator on the dashboard that tells me my a light is out goes on. It turns off when I put on the high beams. As you may know the car uses another wire and fuse all together for the high beams on each side. That annoys me because I think that dummy light (if you will) is absolutely brilliant, it has told me that I had a license plate light out in the past which I may have never noticed on my own and I would like to do this correctly so that light goes it.
A friend suggested that the slightly larger gauge wire we used has different resistance and that dummy light probably comes on when it sees a change in resistance. This makes sense but I wanted to ask the knowledgeable folks on this wonderful forum for some opinions, do you agree or disagree? If it is the wire I need to figure out the right gauge wire because it did not take long to replace, I will just do it again.
Thanks for listening and I hope everyone had a great Christmas/Holiday this year!

frankstallone · #2 12-28-2008, 11:45 AM

UPDATE: I have another friend that mentioned I may have bypassed the load detector saying that the wire going from fuse #13 on the box makes a trip to the load detector first then back to the headlight itself. If so does anyone know where the load detector would be?

sixto · #3 12-28-2008, 02:13 PM

Friend #2 got it. If you powered the headlight directly off the fuse you bypassed the N7 exterior lamp failure monitoring unit. It's the longest box in the aft section of the fusebox, about 4.5 relay units long. Pin 1, a yellow/black wire goes from N7 to the left low beam bulb.

IIRC N7 is the same for all US 124s from 86-90. I'd try a wrecking yard unit before cutting wires.

Sixto
87 300D

frankstallone · #4 12-29-2008, 05:33 PM

Sixto: Thank you for replying back! Very technical explanation too I appreciate that, I figured it might have something like a N7 exterior lamp failure monitoring unit!

Are you suggesting I should attempt to replace the relay?

daw_two · #5 12-29-2008, 07:14 PM

Quote:

Originally Posted by kaiz3n

Sixto: Thank you for replying back! Very technical explanation too I appreciate that, I figured it might have something like a N7 exterior lamp failure monitoring unit!

Are you suggesting I should attempt to replace the relay?

I'll be happy to see if there's one in the w124 300TD in the boneyard.

frankstallone · #6 12-29-2008, 07:19 PM

Well if that relay is just for the driver side low beam then it might be worth a venture but that means there is a relay for each headlight low beam and high beam?

sixto · #7 12-29-2008, 07:49 PM

It's a single relay for all exterior bulbs.

Yes, I think you should try another relay it before messing with wiring.

Sixto
87 300D

frankstallone · #8 12-29-2008, 08:12 PM

Clearly it is a little too late for that. =)

If a relay goes wouldn't all the exterior lights go out?

sixto · #9 12-29-2008, 10:08 PM

Did you do anything you can't unmess?

I haven't heard of a relay disabling all exterior lights. You'll have an annoying warning light.

Sixto
87 300D

frankstallone · #10 01-01-2009, 11:01 AM

sixto your always so helpful!

David you want to see if you can find me that relay? LMK
I didn't remove the wire it is still there I will just solder the pin back on it.

Happy New Years guys!

frankstallone · #11 02-07-2009, 02:55 PM

I got a relay from daw_two and I am going to re-wire it back and see if that works.

@sixto - I read your reply wrong, it is something I can unmess, everything is still there I just have to solder the pin back on the right wire.

Frank

frankstallone · #12 02-07-2009, 04:02 PM

Okay so! daw_two the relay you gave me is next to the longest relay under the hood here (to the left on the photo above). I assume sixto is talking about the one I have circled above which is definitely the biggest relay here. Relay 126 542 01 32 is what I need!

Franksta

Jeremy5848 · #13 02-07-2009, 05:52 PM

The relay in the middle row, in between the one that you have 'ovaled' and the aux fuses, is N10, the "combination relay." It handles the turn signals, the rear window defogger, and the front windshield wipers.

daw_two · #14 02-07-2009, 07:47 PM

Well, it was the longest relay that was in the donor car....

You ought to test it especially if the numbers match, then keep it as a spare or pass "the deal" along to someone else. I'm just glad you got it, we worked out the details of the PayPal notice you got (ck your email), and we now know which relay controls what. Well, maybe we know that.....

You all won't even believe what I saw today.....an NA 300D, 282K miles on it....out in the country.....non running....guy wants $1200.

No rust, but did have a LOT of silicone around the back window. I told him if it weren't so far from Memphis, I would make him a cash offer on it........but he would be disappointed if he really thinks it is worth $1200

Quote:

Originally Posted by kaiz3n

Okay so! daw_two the relay you gave me is next to the longest relay under the hood here (to the left on the photo above). I assume sixto is talking about the one I have circled above which is definitely the biggest relay here. Relay 126 542 01 32 is what I need!

Franksta

frankstallone · #15 02-11-2009, 11:09 AM

Haha yeah I will definitely pass it on to anyone who needs the relay, no need to get rid of a perfectly well working relay.

If anybody does have the right relay or can get it let me know!

Good find btw =D

Quote:

Originally Posted by daw_two

Well, it was the longest relay that was in the donor car....

You ought to test it especially if the numbers match, then keep it as a spare or pass "the deal" along to someone else. I'm just glad you got it, we worked out the details of the PayPal notice you got (ck your email), and we now know which relay controls what. Well, maybe we know that.....

You all won't even believe what I saw today.....an NA 300D, 282K miles on it....out in the country.....non running....guy wants $1200.

No rust, but did have a LOT of silicone around the back window. I told him if it weren't so far from Memphis, I would make him a cash offer on it........but he would be disappointed if he really thinks it is worth $1200