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2000 SLK230
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Discussion Starter · #1 · (Edited)
Hello all,

Have done some significant research across the forums to find out if there's anyway to actually test the all encompassing headlight switch / light module (p/n: A1705450104 I think). So far I haven't had any luck. My problem, which does not appear unique, is the bulb fault light in the instrument cluster. Specifically, my 2000 SLK230 (German spec) fault light comes on ONLY when I switch move the selector to "headlights on" position 2. When in position 1 (park lights only) it doesn't come on. I have pulled every bulb both front, rear, signal, fog and they all work and are the correct wattage (also, no fuses are blown). The odd thing to me, is that it it only appears at position 2, but both headlights (low and high beam) function properly. This nuance would lead me to a problem with the headlights or switch, as all the other lights actually illuminate at position 1 without the fault light coming on. I have seen some comments about possible faulty switch, but was hoping to be able to conduct some sort of testing on the switch / internal workings before having to try to replace it. Wondering if any one has some thoughts on this (putting tape over the fault light is not something I wish to do, in case that recommendation comes out) :smile:. Thanks.
 

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Registered 2003 SLK200
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129 Posts
Mine comes on sometimes. Its related to a dodgy connection of one of the brake light bulb holders.
I don't know if its the left or right yet so I think I will just buy a pair and put a smear of dielectric grease on the contacts.
Driving over a bump is what sets it off.
 

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2000 SLK230
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27 Posts
Discussion Starter · #3 ·
I actually found it quite useful to remove the rear outer lamp lenses (only 3 nuts on either side and the electrical connector), which allowed me to see everything at a glance - definitely worth the minor effort - just don't drop the socket in the well.

You may also be able to then see if it's the bulb in the socket, or the socket mounted on the board. While I had mine off the other week I removed each one, and carefully adjusted the tabs and cleaned them a bit to ensure they all had a good connection. Just a thought. Good luck
 

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2000 SLK230
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27 Posts
Discussion Starter · #4 ·
Today I decided to do a bit of troubleshooting on the wiring harnesses to the front headlamps and fog lamps. Disconnected the ground wire on the battery first, then partially separated the lower and upper console around the steering wheel in order to be able to access and remove the light module (headlamp switch) - 1st picture, I then took off the electrical connectors off the back of the module (2nd picture). Once complete, I sprayed everything with electrical contact cleaner and used a small brush to try to clean the connectors up, although they didn't look dirty at all. The 3rd picture are the actual connectors (left to right: main power loom, multi-purpose connector, front light connector (slightly higher than the others), and finally the rear light connector). My testing used the black large (3rd connector from the left) to test the front light continuity and confirm no short (picture 4).

The colour coded wires (total of 8) within picture 4, starting on the bottom right and moving clockwise:

(1) right headlamp (yellow (ge), white (ws));
(2) left headlamp (yellow/black (ge/sw), white/black (ws/sw));
(3) right headlamp (grey/red (gr/rt));
(4) both fog lights (2 x grey/yellow (gr/ge)); and
(5) left headlight (grey/black (gr/sw)).

You can confirm these by looking at the back of the plug (picture 5). The ground wires from the headlamps / fog lights go to body points in the engine bay.

I confirmed continuity without short within all the left and right headlamp wiring to the harness connection point, and then confirmed continuity from each headlight harness back to the light module plug wires identified above. All had solid resistance and none appeared to short.

This now leads me to believe the problem is within the light module sealed switch:frown:, which I don't know how to test, if at all possible. Will continue to try to figure it out, but above information and the enclosed pictures could be useful to someone.

Should anyone have any ideas, I'm open to suggestion.

Thanks.
 

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2000 SLK230
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27 Posts
Discussion Starter · #5 ·
Wanted to provide an update, or at least my solution for now. After all the testing and removing the lights again, sanding the contacts etc, I found a used Light Module Switch about 40 mins away. Picked it up this morning, installed and problem solved. Confirmed that the problem was in fact in the module itself. 80 Euro solution for the part and my labour of course.

My intent is to try to carefully disassemble the old light module to see if I can figure out a testing methodology for the future. Once / if I am able, my intent is to post pictures and results on this thread. Cheers
 

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Hi, @Skip,

Thanks for that.

I have the same problem and a phone call this morning to a specialist Merc garage elicited the response of it being a 'common' failure, not to mention rather pricey.

I await your update with some anticipation.
 

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Warning: THIS POST IS NOT FOR THE EASILY TERRIFIED.

I've just had a reply from M-B as to price for a replacement unit:

£298. With fitting, if you did not feel capable, this would rise to around £500 as it is a 1.5 hr job.

I'm told that failure of the unit is a 'known weakness' so one would assume that the cheaper option of buying secondhand is a risky one.

I bought my car from a dealer and have had a word with him. As he says, he is obliged to replace the item, but a s/h unit would fulfill his legal requirements. It would seem that he's happy for me to go 50:50 with the price of the new unit and to fit it for free. I will suggest that he supplies the unit and I fit it, but I don't hold out much hope.

On a practical note, how does one remove the vent above the dial?
 

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2002 SLK32 AMG
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522 Posts
Harvey, if the car is going to be a keeper, I'd be quite happy to go 50-50 with the dealer for a new unit. But be aware that if you fit it yourself, that may well invalidate any guarantee that comes with the new unit, as far as the dealer is concerned anyway.
 

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Registered 2005 SLK350-sold
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997 Posts
I removed that warning bulb from the cluster sometime ago, as I use LED's in fogs and parking lights. Easy fix :) Old cars didn't have that feature anyway.
They had it as an option on some cars back into the 1960s. 50 years is "old cars" They had basically a fiber optic than ran to an indicator on the rear deck so you could tell that your rear bulbs were working. And Chrysler had a electronic version back at least as far as 1984.
 

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*Premium Member
2005 SLK55 AMG /2005 SLK350
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6,867 Posts
Harvey,

There is a screw at the top of the vent - you won't see it unless you adjust the plastic airflow mechanism "high".

Mercedes-Benz SLK 230 Lower Left Dash Panel Removal | 1998-2004 | Pelican Parts DIY Maintenance Article

If you've never removed the light module before, it's kind of tricky, and the plastic lugs are prone to breakage. I suggest you have an assortment of cardboard boxes and a helper at hand the first time you do it. Use the cardboard boxes to hold the knee panel after you've freed it but before you've disconnected the electrical wiring. And don't force anything - there are lots of well-hidden screws you have to remove to free the knee panel.
 

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I appreciate that, efair.

I keep a clean garage. I once went to research an article on a racing team, LNT, run by the bloke who bought Ginetta Cars, Lawrence Tomlinson.

The floor of the workshop was immaculate. In the working areas there was a thick lino type substance that was unmarked. I mentioned to him that it must be nice when, after dropping a nut on the floor, when you found it you didn't have a choice. He didn't find it amusing.

Lawrence (worth over £500 million last I heard) was very pleasant to me and let me drive his T440. See picture. Just look at the floor. If you ate your tea off it you'd put a tablecloth down so you didn't dirty it.

At that time he was trying to buy TVR but had his Ginetta G4 at the back of the workshop. When I said I had a Ginetta G32 as well as a TVR we became buddies.

When I returned home I covered the floor in my garage with chipboard and then lino, right up to the walls. It changed the whole atmosphere. I felt as if I knew what I was doing. Well, almost.
 

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Discussion Starter · #15 ·
Also being very careful when removing any of the panels, if colour matched or painted, as it is easy to scratch / allow to peel. I've been happy with my recycled part (30 day warranty) with no issues, but I expect it is hit and miss with such things.
 

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Hi, Guys,

I have had a chat with the dealers and he accepts that a new switch is a reasonable request. I had an idea of what would be a reasonable outcome and he came back spot on, so I happy. Mind you, I'm also poorer, or will be when it is replaced.

I write on consumer law off an on and the advice I often suggest is pick whom you do business with with care and discuss liability at the beginning. Nice to know I'm not talking rubbish.

I hope it is OK to give the name of the dealer I bought the car from. Maple Leaf Cars Ltd - Used car dealership in Billingshurst
 

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I've just had my headlamp switch replaced with a new unit.

The garage quoted £472.63 (very precise price) for the replacement but as it turned out it went smoother than they expected and I was charged £430. I have since discovered that the dial is illuminated so a positive, if somewhat expensive, outcome. Ironically, I moaned when the replacement headlamp bulb I put in didn't illuminate as I thought I'd have to buy two new ones to have one as spare. To add insult to financial injury I threw the bulb I thought was defective into a metal bin I keep in the garage. It broke.

I've got the old light unit and will open it up in the near future to see what makes it tick. Or in my case, not tick. I'll post pictures of it.

So an irritation. I thought one advantage of the 170 over its replacement was fewer electronic devices to go wrong.

And I've just discovered that there's a warning light for the reservoir for the windscreen washer fluid level. You live and learn.

Anyway a result. I don't like being illegal.
 

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*Premium Member
2005 SLK55 AMG /2005 SLK350
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6,867 Posts
Advantage: fewer electronic devices to go wrong. :)
Disadvantage: electronic parts are older :(

I'm on my fourth R170 "fixer upper" and I've not yet seen a bad light module. I bet it has the usual-suspect relays in it - anxious to see the pics.
 

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Advantage: fewer electronic devices to go wrong. :)
Disadvantage: electronic parts are older :(

I'm on my fourth R170 "fixer upper" and I've not yet seen a bad light module. I bet it has the usual-suspect relays in it - anxious to see the pics.
I'll probably start over the weekend with the dismantling.

The garage said it's a relay.

I had a problem with my first SLK, I won't say which one as I see you have a 171 350, was with the rain sensing wipers. I asked a garage what the problem was. His reply was that the major problem was the cost.
 
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