Horn inop except with H/beam &...

[John Jones Jr]

Hoping somebody can assist, '98 W202.

I've two problems, I think? Originally, my first problem was the n/s main beam would not work at all and the o/s would not flash and no main beam dash warning light. So, I found a fuse gone, No.34. (7.5amp) which is for the n/s main beam & dash warning lamp. Fuse replaced and both main beams working and flashing also dash warning light working too but... the horn operates now while using main beam! The horn will not work otherwise.

Also, at the same time combi the switch failed to work, on indicators & windscreen wash/wipe. Actually it blew fuse No.22 (10amp) as I tried to operate the wash/wipe.

Now, why I'm unsure if I've got one or two problems, simply because the windscreen wipers, w/wipe, indicators & headlamp flasher all share fuse No.22.

Just add, I replaced No.22 fuse and wipers, indicators & main beam (with horn) all work. Fuse only blows when w/wash is operated.

Any ideas or advise greatly received.

 

[John Jones Jr]

Update:

Replaced the steering column combi switch (wipers/horn/indicators/main beam), no fuses blowing now - great but...I still have no bloody horn! The horn only works when main beam is activated.

Horn relay is clicking when horn buttons pressed.
Horn wiring in steering wheel looks o.k.

An earth problem?

 

[John Jones Jr]

Latest update:

Just checked the horn fuse. Surprised to find that there's two fuses and one was blown. Replaced fuse now the horn is working at the steering wheel, happy days.....but the main beam comes on too. And horn still comes when main beam used!

 

[boxbrownie]

Latest update:

Replaced fuse now the horn is working at the steering wheel, happy days.....but the main beam comes on too. And horn still comes when main beam used!

Sounds like an option for Italian City driving

 

[John Jones Jr]

Funny you said that, I was thinking it might be worth while to have the main beam flash whenever the horn is pressed - just for those drivers that are hard of hearing!

 

[grober]

Think you have an earth problem as you surmised

 

[renault12ts]

Defo an earth problem...all sorts of weird and wonderful things happen with a bad earth.

 

[Bryan Allman]

Latest update:

Just checked the horn fuse. Surprised to find that there's two fuses and one was blown. Replaced fuse now the horn is working at the steering wheel, happy days.....but the main beam comes on too. And horn still comes when main beam used!

That is a cracker

 

[John Jones Jr]

Think you have an earth problem as you surmised

Cheers Grober, yes I reckon it is, just good to hear the same thing from somebody else. Especially as my original problem was actually (it seems) two faults that were linked by common fuses. Anyway, thanks be I'm down to one fault now :bannana:

I've looked for the earth point up front and have found two multi earth points both on each inner wing. Any idea if there's more?

 

[John Jones Jr]

Defo an earth problem...all sorts of weird and wonderful things happen with a bad earth.

R12ts, music to my ears, cheers.

 

[John Jones Jr]

That is a cracker

Electrickery

 

[BlackC55]

Defo an earth problem...all sorts of weird and wonderful things happen with a bad earth.

I agree too.

 

[John Jones Jr]

Cheers Olly.

You don't happen to know where the earth points are for the horn & lights? I cleaned all the earth points on both inner wings, one on the o/s and two on n/s but there was actually nothing wrong with them anyway.

 

[RBYCC]

Possible a back fed circuit or earth through the clock spring / contact ring in the steering column ?
Also check if the horn button return springs are sticking.

http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1996/C280/SYSTEM WIRING DIAGRAMS/5808.pdf

 

[John Jones Jr]

Thanks RBYCC, you could well be on to something there. I'm just hoping it's either a bad horn or h/lamp earth at their earth points. I'll know soon enough when I locate both. If both are wired anything like the W201 then I reckon I'm on a winner.

 

[Ted]

Does the main beam come on full brightess when the horn is used?
If so, I doubt it is an earth problem, and is more likely to be a supply issue (i.e. horn and main beam wires connected together somehow)

Most supply issues (especially on Mercedes) are where the wiring has been tampered with - maybe there is an aftermarked alarm fitted that blows the horn and flashes the headlights which is faulty?

 

[John Jones Jr]

Interesting Ted. Yes, the main beams are full brightness or seem to be when the horn is activated. And there's no retro fit alarm installed, from what I can tell. I've had a good luck at the wiring under the steering column and in the engine bay - nothing to indicate that anybody was messing with the wiring.

Now, I've just gone and checked the operation of the standard alarm system. All working as per the owners handbook, EXCEPT the the 'Acoustic alarm' (i.e. the horn I presume) does not sound intermittently for 30 seconds as it should, unless I'm doing something wrong when I was trying activate it?. So Ted, you may have very well got me on to something here or else sent me off on a tangent

I'm now wondering would a faulty SAM unit be the culprit??????

 

[RBYCC]

Thanks RBYCC, you could well be on to something there. I'm just hoping it's either a bad horn or h/lamp earth at their earth points. I'll know soon enough when I locate both. If both are wired anything like the W201 then I reckon I'm on a winner.

If the horn(s) operate, regardless of however, it would tend to negate an earth problem at the horn location in the engine bay.

The horn circuit has power on the horn relay coil and is completed when pressing the horn switch which goes to earth.

The horn working with the main beam would tend to indicate a problem somewhere between the relay the steering column switches.

What's interesting is that you get a "clicking" when you press the horn switch.
Are you sure it's the horn relay, have you checked voltage at pin 4 with the switch depressed?

There is no normal circuit connection between the horn and main beam.
The only "sharing" is in the harness into the steering column.

More then likely the earth or short is in this area.

Poster "Ted" brought up another theory concerning the factory or aftermarket alarm which with age tend to be problematic.

Ed A.

 

[John Jones Jr]

Thanks again RBYCC. Yep, for sure it's horn replay kicking in as the horn now works from the st.wheel buttons after replacing one of the horns two fuses which was blown.

If we presume you are correct and it's a problem at the harness around/near the steering column, which I've inspected to the best of my ability I may have no choice but to use an auto electrician but I may just pull the lower st. column panel again and have an other look first.

What do think about the standard alarm system not activating the horn?

 

[Dec]

Thanks again RBYCC. Yep, for sure it's horn replay kicking in as the horn now works from the st.wheel buttons after replacing one of the horns two fuses which was blown.

If we presume you are correct and it's a problem at the harness around/near the steering column, which I've inspected to the best of my ability I may have no choice but to use an auto electrician but I may just pull the lower st. column panel again and have an other look first.

What do think about the standard alarm system not activating the horn?

Your alarm has most likely expired, I doubt it has anything to do with your original problem but you could disconnect the alarm siren any way, read this post first, see here… http://www.mbclub.co.uk/forums/electronics/150666-something-draining-my-battery-my-c43.html

Dec