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1980 350SL: headlights..windscreen wipers come..fuse box..connector…

Customer Question
Hi, when I switch the...
Hi, when I switch the headlights on on my 1980 350SL the windscreen wipers come on as well! Do you any ideas on where to find the problem in the wiring?

I have replaced the indicator/high beam stalk switch 2 years ago when this problem was intermittent - it cant have been the problem - also back then I totally cleaned out and tidied up the fuse box area which had got some moisture in it, also checked the connector for the indicator stalk switch to the main loom. Now, this problem is no longer intermittent - it happens everytime I switch the lights on, also strange things happen when I switch the high beam on. I have checked the fusebox and the indicator switch yesterday and all seems OK.
Submitted: 8 years ago.Category: UK Car
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Answered in 1 hour by:
6/27/2010
UK Auto Mechanic: Mike, UK Car Mechanic replied 8 years ago
Mike
Mike, UK Car Mechanic
Category: UK Car
Satisfied Customers: 39,198
Experience: Hi, I am a Car/ vehicle technician of 34 years. 29of -running my own repair/diagnostic business.
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Hello and Welcome to justanswer..

This is generally a switch problem to be honest...

I realise why you are hesitant.. but 99/100 it is... Basically because the switch is worn inside ( nothing to see mind )... when you operate the switch - you get the double function..and sometimes more !

You can verify it by removing and testing the circuits behind.. ie, probing to activate the circuits say, the headlights...and of the wipers don't come on ( as I suspect will be the case ).. then you know its the switch inside thats causing all your problems here ...

A replacement switch is the answer to that one...... ;)

I Sincerely XXXXX XXXXX have helped you - Please ask me if you need more help...


Kind Rgds, MIKE

 

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Customer reply replied 8 years ago
Hi Mike, thanks for your answer, I could try to activate the lights without the switch but to do this I need to remove the light switch unit in the 1980 Mercedes-Benz 350sl. I cannot see how I can get this out, do you know how to remove it? do you have to take the dash board out? I was trying to do this but I could undo the steering wheel bolt to take the wheel off to access the bottom section of the dash. Is there a trick to getting the light switch out?

kind regards

Richard
UK Auto Mechanic: Mike, UK Car Mechanic replied 8 years ago
Hello again Richard.... thank you for your reply...

Sorry , I was referring to the multi function switch as the problem one - not the single rotary headlight switch - the one you mentioned in the original question... Thats where I believe the fault to be.. So thats the one to be concentrating on ...

If you need more help please do let me know - in case I misunderstood you ...

Best Rgds , MIKE..




  • >>>>>>>>>Please don't forget ....Please press the ACCEPT button if you are happy with my answer/advice given -as that's how I get paid for my time ... Thank you...

 

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Customer reply replied 8 years ago
Hi Mike,
I would like to send you a couple of attachments to show how the multi function switch is testing - how can I do that?

Kind Regards

Richard
UK Auto Mechanic: Mike, UK Car Mechanic replied 8 years ago
Hello again Richard..

Thats fine... See the "you tube" icon above in this box.... click the icon just to the left of it...

Click the browse button.. that will open another box - click the browse again and load it up from your computer - click ok - then in the other box - click "insert" - and it will load up..

Just a tip - when you click the box buttons - wait for the box to close - don't rush the browser or it will fail the upload..

Best Rgds - MIKE.

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Customer reply replied 8 years ago

graphic

 

graphic

 

 

graphic

 

OK Mike the top picture is the back of the connector from the multi function switch which plugs into the female from the loom (second picture).

 

The image below that shows the results of my testing.

 

The bottom left and right terminals are for the main lights. The second from the top two terminals are the wipers.

 

1. With the ignition off (A) there is power only to terminal 5 (fifth down on the left) and everythin on the right except the top terminal goes to earth.

 

2. With the ignition on (B) we now have power to the windscreen wiper switch and another terminal (4th down on the left).

 

3. With the ignition and side lights on (C) (switched from the rotary light switch) its the same.

 

4. With the ignition and main lights on (D) (switched from the rotarty light switch) we now have power to the bottom left hand terminal.

 

SO - to test the multifunction switch - if there is a connection between the bottom left terminal and terminal 2 - or terminal 9 - then that would prove that when power was on at terminal 7 forthe main beam, it was also being passed to the windscreen wipers right?

HOWEVER - when I test the multifunction switch in its off postion (which is when the when the wipers come on when you switch on the main beam) I find that there is no connection between 7 and ANY of the other terminals except 14 which is permanently connected. Also 3 and 9 are permantently connected.

So doesn't this mean that the connection between the lights and the wipers is being made some where other than the multifunction switch?

 

Also - please note that if the switch is faulty, it would be the second multifunction switch to fail in 50,000 miles - which seems unlikely for mercedes.

I have a multi meter - what do you think I should test from here?

 

Kind Regards

 

Richard

 

UK Auto Mechanic: Mike, UK Car Mechanic replied 8 years ago
Hello again Richard - thank you for your reply and info -

I have looked at this above two or three times which is why its taken me a little while to get back to you - Ive been studying it !

As I see it - because the problem is as it is.... If you use a power supply from the plug ( any) and link it to the output for the headlights .... if the headlights come on -on their own...without the wipers.... then that identifies the switch as faulty - as its been taken out of the equation for test purposes / bypassed...

I know that sounds somewhat simplistic - but given all that you have you said and done as above... that will ID it for sure..

If the wipers were to come on doing that - is a problem further down the line - either a short in the wiring / fuse or relay box...which would then need further investigation...

I believe you will likely find its the former as the problem - but thats the way forward now on this one to ID it for sure..

I hope that helps you further -

Best Rgds - MIKE



 

  • >>>>>>>>>Please don't forget ....Please press the ACCEPT button if you are happy with my answer/advice given -as that's how I get paid for my time ... Thank you...

 

Feedback and any Bonuses are always appreciated too. Thank you.





















Edited by Mike on 6/30/2010 at 8:20 PM EST
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Customer reply replied 8 years ago
Hi Mike,

I removed the two bottom wires (7 and 14) from the back of the connector on the multifunction switch - I then plugged the connectors together (with the two bottom wires removed.) I then bridged the terminals 7 and 14 of the connector from the loom with a piece of wire - thereby by-passing the switch.

I then switched on the lights and the windscreen wipers came on - the fault was still there.

I think this proves the fault is somehwere else - do you agree? if so where else should I look - if not what now?

Kind Regards

Richard
UK Auto Mechanic: Mike, UK Car Mechanic replied 8 years ago
Hi there Richard.... Thank You for your reply...

Indeed I do agree yes... the test routine has proved that ....

Now, it could be a short in the wiring or a fault in one of the models....

Unfortunately for this age of motor I don't have much info at all on the electrics / modules etc... you really will have to obtain that from a manual or source - but for you sure - that does discount the switch. A good result so far..

I will try and obtain any info I can for you ...and I will get back to you with it if I can...but if you do have or can get a manual that would be good..... but its going to come down to testing through the wiring.... A common problem that can cause this generally is a short inside the fuse box...Im talking generally with other makes / models - and it would make sense with this...so - I would turn my attention to that now ....

Let me know how you get on Richard...

I hope the above helps you further some..

Best Rgds - MIKE.



 

  • >>>>>>>>>Please don't forget ....Please press the ACCEPT button if you are happy with my answer/advice given -as that's how I get paid for my time ... Thank you...

 

Feedback and any Bonuses are always appreciated too. Thank you.

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