W124 convertible Sun Visor

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ash_2009

Active Member
Joined
Aug 28, 2009
Messages
155
Location
London
Car
C36 AMG, Past W124 E220 Convertible
Hey All,

Any ideas on what could be going on here???

I have a issue with my DRIVERS side illuminated sun visor. It just doesn't light up:wallbash:. Its a W124 e220 convertible.

So this is what I have done so far.

1) Changed the bulbs and I did this twice with new ones from MB dealer.

2) I used a volt meter and measured the voltage at the clip (left hand side of sun visor), where it can be pulled in/out and has two metal contacts, and I got 12V coming through.

3) Further I measured the voltage at the bulb holding points on both bulb holders, shown by a RED arrow, with both the SWITCH (blue arrow) closed and open...and this is the funny part....if I remove the bulbs I get 12V fine with the switch closed and when I measured at the same point with the bulbs in position and switch closed then I get no voltage at all...and the bulbs DON'T light up!!!

4) I also replaced the switch and the same thing as above is happening with the voltage.

Any ideas....

Ash
 
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Use a test light rather than a voltmeter.
You will get misleading results using a voltmeter.
 
A voltmeter measures the voltage and in doing so draws an extremely low current. Thus (Ohms law) any high resistance doesn't reveal itself, as it doesn't show the actual voltage over the 2 points you're testing.

Its probably the fuses, they and the contacts in the fusebox are notorious for getting dirty/corroded, leading to high resistance and voltage drops. A sensible approach is to thoroughly clean up all the connections and replace all the fuses with new ones, given the price of fuses.
 
Sorry to sound so stupid...but where can I find a test lamp/or make one myself.

Thanks

Try with a test lamp instead of a volt meter.
 
I did check the fuses and all seemed okay...but I didnt clean or replace them. I shall give that a go later on. I would have thought if the fuses were bad/corroded then the visor on the passengers side would also NOT work...but it does:eek:

A voltmeter measures the voltage and in doing so draws an extremely low current. Thus (Ohms law) any high resistance doesn't reveal itself, as it doesn't show the actual voltage over the 2 points you're testing.

Its probably the fuses, they and the contacts in the fusebox are notorious for getting dirty/corroded, leading to high resistance and voltage drops. A sensible approach is to thoroughly clean up all the connections and replace all the fuses with new ones, given the price of fuses.
 
Halfords sell cheapo ones. You can make one yourself, but they are cheap enough.

As has been said, a testlight will put enough load on the circuit to test if there is enough current available to work whatever you are testing.

A voltmeter is for measuring voltage (surprisingly enough!) e.g. testing charge voltage.
 
A voltmeter measures the voltage and in doing so draws an extremely low current. Thus (Ohms law) any high resistance doesn't reveal itself, as it doesn't show the actual voltage over the 2 points you're testing.

Its probably the fuses, they and the contacts in the fusebox are notorious for getting dirty/corroded, leading to high resistance and voltage drops. A sensible approach is to thoroughly clean up all the connections and replace all the fuses with new ones, given the price of fuses.

I have cleaned all the contacts and also replaced all the fuses with new ones and still the sun visor doesn't light up:wallbash:

Any one with some other ideas please.
 
Make sure you have power @ fuse and trace the break from there.
 
Sounds like you don't have a negative, did you check for a break in the negative wire. I am not familiar with this type of visor, what way are the wires connected around the swivel area ?
 
It most likely is high resistance as stated, this could be on the 12v supply side or ground. However as you read 0v on the supply when the bulb is inserted suggest its on 12 side.

try to power the visor with a feed directly from the battery. Unclip the visor so the original supply is isolated. For saftey you can fuse the feed if required.
you can also try the opposite and short the ground side of the bulb to see if the high resistance is on the ground.

Once you know where it is youll have to check at any junctions on the circuit to find and eliminate the high resistance. Which is probably beinh caused by a corroded connector or joint.
 
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