R129 failed dip beam

[RichardF]

Everything else works okay no warning lights? Anyone else had this? Switch Relay? where should I start to look?

 

[Sp!ke]

Checked the fuses?

If they are ok, are you getting 12v feed at the appropriate fuse when dipped beam is on?

That's where I would start... follow the voltage to or from the fuse depending on whether you have a feed or not.

 

[RichardF]

Thanks. It was dark when I got in so not checked the fuses yet, I will try to find some time tomorrow. L & R are fused independently so I'm thinking it will be "upsteam".

 

[RichardF]

No power at the fuse. I won't have time to touch it till monday now, I will try to enlist some help.

 

[Sp!ke]

Obvious thing to look at is the switch itself then inside the car.

 

[RichardF]

I had time to pull the light switch out all seems ok, could it be the dip switch?

 

[V12]

I'd guess at the stalk.

 

[RichardF]

I think you may be right, is there a guide to get it at it? (the stalk that is)

 

[Sp!ke]

going from memory you need to undo the steering column shrowd (handful of screws) and then you can unplug and detatch/test.

 

[V12]

The plug goes further down the column from memory, you need to drop the under dash panel to access it.

 

[Dec]

What year is the car?

Does the high beam and the high beam flasher work?

Do you have number 3 in the picture below? I think it’s the lighting control unit?

Dec

 

[RichardF]

Hi beam and high beam flasher work okay. It's a 94M 320, my fuse box looks a little older with torpedo fuses. I haven't opened up the box behind the fuses yet.

 

[Dec]

My understanding is that when you turn the dipped lights on, the stay on until you turn them off again, at the main light switch.

The stalk stick is a 4 way lever switch, up/down for the indicators and in/out for the high beam/flash high beam, the stalk switch doesn’t play any part in switching the dipped beam ON or OFF, in other words the dipped beam is on all the time when switched on at the main light switch, and stay on, with or without the high beam/ flasher beam being used.

Do the fog lights work ok, front and back, and the tell tail orange light, when the back fog light is on?

Take note of the part numbers on the long relays at the back of the fuse box, useful to identify what you got.

A rusty/bad earth for the dipped beams could also explain the fault, if the fuses are definitely not causing the fault.

Double check those old type fuses, the have a bad reputation see… Check ALL fuse boxes - Mercedes-Benz Forum ...American car so fuse box is on opposite side of car.

Dec

 

[RichardF]

Thanks for the reply.
All the other lights (fogs, sidelights, parking lights tel tail etc)
If a bulb is out the warning on the dash illuminates (not for the dipped beam however)
I've cleaned and swopped fuses. At one point I seemed to be getting 13v to the fuses although no dipped beam on.
I don't think it's a fuse problem because both lights are effected. Do you suspect the lighting control unit?

 

[Ted]

Don't use a voltmeter to test as these can give misleading readings - use a test light. That will lead you to the problem.
Long shot I know, but it could be that both bulbs are gone - I have seen it where a bulb fails, the driver doesn't notice for a while, then the other bulb goes and you certainly do notice.

 

[RichardF]

Thanks for the tip. I use a test lamp and a multi meter.

The bulb failure warning seems to work ok (does not come on for the dipped beam)and I've checked the bulbs, no power at bulb holder or L&R fuses.

 

[Dec]

Open up the lighting control unit and examine it with a good strong magnifying glass for signs of broken solder, corrosion or damaged PCB tracks, don’t know what’s inside the unit but suspect it comes out and will be similar to the N10 relay, example here… N10 Relay, Soldering Repair, Wiper - Indicators & Hazards - Rear Window Demister. - Mercedes-Benz Owners' Forums

eBay example… Mercedes R129 95 02 SL500 SL320 SL600 Hella Lamp Control Module 1295420432 | eBay

Dec

Edit, before you remove the unit, try rocking it from side to side while the dipped beam is ON to see if the dipped beams light upn, this might or might not indicate a bad joint inside the unit.

 

[RichardF]

Thanks for your help.

I've opened the box and had a "waggle" my fuse box is older so the control units are in different places. I'm now out of time this weekend, family things to attend to.

Monday I should be able to enlist some knowledgeable help so will have another go then.

 

[RichardF]

Looks like it is the lighting control module. Waiting to see if it can be repaired or new one is required.

 

[Dec]

Got a picture or can you describe its internals... just curious.

Dec