W115 1974 240D Brake Lights not working - Mercedes-Benz Forum

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post #1 of 6 (permalink) Old 06-01-2009, 12:49 PM Thread Starter
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Vehicle: 1974 W115 240D
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W115 1974 240D Brake Lights not working


I recently purchased this car and the right brake light doesn't work and sometimes both don't work. There is water damage and surface rust in the trunk from the leaking old trunk lid rubber seal so I think it may be a ground issue as I have replaced all the bulbs and fuses. I have the owners manual and the Chilton book but neither have a wiring diagram - any help or advice would be great.

Also, I got new trunk rubber but what is the best product to glue it in place? Any tips on cleaning the surface first?

Thanks, Paul.
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post #2 of 6 (permalink) Old 06-01-2009, 09:18 PM
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make sure all the wire connections are good and not rusty. You may just have to replace the wires.

My brother was having a similar issue with his '73 toyota landcruiser and had to replace a good chunk of the rear brake light wiring. In his case a bunch of the wiring was hanging/clipped to the bottom of the frame at the rear end so it was pretty exposed to the elements, and it doesn't help that it was a hunter's truck before that and the whole vehicle was a bit "mickey moused"

Hope you get to the root of the issue, but intermittent electrical problems can be the worst, so check the grounds and connections, and replace wiring if need be, and be prepared to take your time, and don't drive the thing without working brake lights!!!!!!!!!!!! Dangerous, and you'll get a ticket.

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post #3 of 6 (permalink) Old 06-02-2009, 07:39 PM
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I have a wiring diagram and it says that there is a brake light switch. I haven;t look but I suspect that it is actuated by depressing the brake peddle. If cleaning the connections doesn't work you may save yourself a bunch of frustration by just running a new cable from the switch to the brake lights. THe diagram says the wire to the brake lights is is black and red. I'm getting this from the "Chilton;s import automative repair manual" Good luck.
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post #4 of 6 (permalink) Old 02-25-2010, 05:01 AM
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I've had a 115 240D for a couple of years now and the tail and brake lights are becoming a nuisance. There's no problem with the switches or wires as I am able to get them to come on without fail when I jiggle the bulbs (with the lens assembly (cover) off. They sit slightly loose in the sockets. I've used conductor goop, I've bent the metal tab at the base higher to get better tension and generally mucked around with them for waaaay too long. The best result I've had is to wedge a small piece of paper along the side of the bulb base to snug it into the socket. I'm sure this is some sort of fire hazard but it works.
So, please help if you know: Do the aftermarket auto supply stores have the wrong bulbs listed and they're just shining me on? I don't want to buy $35 bulbs (just guessing here, a new key from the dealer was going to be $60!)
Is there something I'm missing on the socket maintenance?
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post #5 of 6 (permalink) Old 03-05-2010, 04:30 AM
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No answer yet . Would really like some help here. Seems like it might not be a rare problem.
Meanwhile, I've thought of another solution. I think one of those retrofit third brake lights would help. I'd also like to know if anyone has experience retrofitting new lights into place. Like maybe drilling out the old sockets and adding LEDs or something.
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post #6 of 6 (permalink) Old 03-22-2010, 11:13 PM
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I think the switch is activated by pressing on the break pedal and completing the connection. I would trace the wire all the way from the bulb socket to the break pedal and check for any damage to it along the way. Also check the connection at the break pedal if you can find it... i have no idea where it could be. You may be able to cut the wires at the bulb socket and re wire for a new bulb socket type by splicing the wires if a loose bulb socket is the culprit. My car was flooded to the dash and the headlight switch had to be replaced. This ran the parking lights and headlights, as well as lic. plate light. Not sure if it ran the break lights too or if it tied into them somehow, but I would take the switch out of the dash and check for loose connections there too to be on the safe side. These are just suggestions though, and my educated guess at best. Hope this helps you.
I replaced my trunk seal with a silicone adhesive and it seemed to bond well to the groove that it sits in. My old seal came out pretty easily and I scraped down and removed the rest of the rubber with a file. It fits in the groove a certain way and fans outward to make a seal with the lid.
It may be that after years of wear the break light sockets are just loose, or they may just be selling you the wrong bulb. I was hard pressed to find the exact same bulb for my front yellow park light under the turn signal light, and even though the bulb was a different shape it still worked. I think they still sell the whole break light assembly so that may be something to look into if you want to keep it vintage. You shouldn't have to go through the dealership either... there are plenty of resources on line to find it I am sure. If not though, i am sure it wouldn't be too hard to retrofit something in. I would keep the covers the same if your going this route and just change the insides, imho (in my humble opinion).
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