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1988 Mercedes 560 SEC (UK spec)
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166 Posts
Discussion Starter #1
Hi,

My reverse lights suddenly went out last week. I have the W126 service manual volumes 1 and 2... but I can't find anywhere in them that actually shows the wiring diagram for the lighting, or the pinouts on the rear lamp clusters.

Both reverse lights are out, both bulbs are OK and all my other lights seem to be working fine. Does anyone have any ideas, or could point me in the direction of the right wiring diagram? I've tried searching the forum but have had no luck.

Thanks,

Chris.
 

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Two '87 570SECs, one '87 560SEL
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4,438 Posts
It's probably the reverse light switch on the side of the transmission is out of adjustment. Have someone watch the lights as you slowly shift from Park to Neutral and see if they come one somewhere in the travel.

I don't know how to adjust it, but since my 560SEL already has this problem, I'd be interested in the solution myself.
 

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German Stuff
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80 Posts
+1 on the switch if both bulbs are fine and won't light. I've replaced one on a BMW before, took me all of 30 minutes tops from pulling the jack & stands out to putting them away. The most difficult part is crawling under the car and getting your hands in the right place.

If you're feeling lazy I'm sure a decent MB shop will do it for 1/2 hr of labor, and even then they'd be charging more time than it takes them.
 

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1988 Mercedes 560 SEC (UK spec)
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166 Posts
Discussion Starter #4
thanks a lot for the replies, I'll get under the car and have a look.. is it easy to find the switch?

Cheers,

Chris.
 

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Premium Member
2012 CL550 4MATIC Coupe
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9,985 Posts
The ETM (Electrical Troubleshooting Manual) is a separate volume.

PM me your email and I will point you to it.
 

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1988 Mercedes 560 SEC (UK spec)
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166 Posts
Discussion Starter #6
Mcclare, thanks for sending through the ETM.

I haven't had a chance to look yet, but I did 'accidentally' test out something - I'm not sure if this proves it's actually not the switch causing the problem.

When I was trying to figure out what was wrong yesterday, I accidentally left the gearbox in Reverse. When I tried to start the car this morning, it wouldn't start - because it was in Reverse gear! I pulled it back into park and it started working fine.

Now, I thought maybe there's a backup switch for reverse, and then park switch to lock out the starter unless you're in Park.

However, looking at the ETM, it seems that the switch is the same switch for backup lamp/start lock-out.

Is it likely that the switch could fail for the backup lamps, but still work for the starter lock-out? I guess it must be different contacts on the same switch, so I suppose it's possible, but I'm kind of guessing.

I might have time to get under the car tonight and have a look.

Chris.
 

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German Stuff
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80 Posts
Not sure on the Merc, but on any other car the switch would be completely different. It should be a switch that keeps it from starting when it's in *anything* other than P or N. The reverse light switch should be only active in R. Totally different functions, can't imagine it being the same.
 

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Always Remembered RIP
1991 560SEC AMG
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10,146 Posts
RAB Motors Mercedes Benz, San Rafael CA. Dealer invoice 04/08/97

had to dig deep for this one, in the records.. but here it is:)

91 Mercedes Benz 560SEC mileage 54,230 lic. # 3KQE535

Electrical System

Customer states reverse lights inoperable. Check and advise.

Found and replaced burned fuse. Found loose connection under fuse box for fuse #5. Removed and reinstalled glove box, retightened connector.


Never had a problem again, after the Mercedes dealer fixed it for me almost 13 years ago.
 

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1988 Mercedes 560 SEC (UK spec)
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166 Posts
Discussion Starter #9
Cascade, thanks a lot for the extra info! I thought the bulbs were on the same fuse as the other exterior lights - it all looked fine, but I didn't really check too closely as I just figured everything else was lighting up fine. I'll check it out and have a closer look this time...

I didn't have time to get under the car last night after all - I'll give this all a proper look-over now and report back what I find. Not sure about the glovebox reference as my car is RHD - I don't know if I'll find the same connectors behind there.

E36 - I would have thought the same as you, but it definitely looks like the same switch from the wiring diagrams. I think basically it's a multi-position switch with connections for the various gearstick positions. The connection when in the reverse position lights up the back-up lamps, the connection when in park completes the starter circuit.
 

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83 500SEC, 84 300TD, 86 190E 5.0 M113, 87 300D, 01 CLK55, 02 C32, 02 C320T, 03 C320T4, 03 E55
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2,600 Posts
Chris, there are two sets of contacts inside the neutral saftey switch, one as stated for your reverse lights and one for starter lockout. In my last case, one of the contacts inside had fallen out of its spring and wasnt allowing the power transfer through the switch to the lights. If you can wait a few hours I can post up a pic of the insides of mine to give you a better idea. Its easily repairable.
 

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Always Remembered RIP
1991 560SEC AMG
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10,146 Posts
'88 560SEC fuse diagram

Cascade, thanks a lot for the extra info! I thought the bulbs were on the same fuse as the other exterior lights - it all looked fine, but I didn't really check too closely as I just figured everything else was lighting up fine. I'll check it out and have a closer look this time...
1988 Fuse Diagram <----This could be printed out and tucked under the fuse box lid. It is almost to scale, like a photo of the original for your car, if yours has gone missing.
 

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1988 Mercedes 560 SEC (UK spec)
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166 Posts
Discussion Starter #12
john and cascade - thanks for the additional info. That's really helpful.

John, if you do have a photo of the part I'd really appreciate it. No worries if not, so long as I can find it and get it apart I should be OK.

Nice to know there's so many helpful people here, hopefully once I've spent a bit more time working on my car I'll be able to give something back!

Cheers,

Chris.
 

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83 500SEC, 84 300TD, 86 190E 5.0 M113, 87 300D, 01 CLK55, 02 C32, 02 C320T, 03 C320T4, 03 E55
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2,600 Posts
Chris, here's the pic. Its off my 91 300D but similar internals apply. You can see the two sets of contacts. I removed the switch, ground off the rivets, repaired the contacts and then used screws to put it back together.
 

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1988 Mercedes 560 SEC (UK spec)
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166 Posts
Discussion Starter #14
solved!

John - thanks for that picture.. it looks a bit different to how I imagined from looking at the wiring diagram :)

But - I have it solved without needing to get under the car after all... this is slightly embarrassing really, but when I checked the fuses in the first place, they all looked good. Today I took a closer look at fuse #5 - it looked fine, I took it out, put it back in, and the reverse lights started working!

All the fuses look pretty old. I guess the contacts are getting a bit corroded and it just needed re-seating. I should've thought about it. Just before Christmas I got stuck driving in snow with no windscreen-wipers - that was exactly the same problem with a different fuse.

The only thing that's bothering me is it seems like an awful lot of stuff all goes through that fuse.. including the water pump?! I can't quite believe it was all not working, as I've been driving the car daily - I did about 60 miles in it yesterday alone.

Thanks for all the help,

Chris.
 

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83 500SEC, 84 300TD, 86 190E 5.0 M113, 87 300D, 01 CLK55, 02 C32, 02 C320T, 03 C320T4, 03 E55
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2,600 Posts
auxillary water pump, your main water pump is belt driven.
 
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