[W126 Coupe] dim passenger light

[millerlh at earthlink.net]

I am no expert at all in these matters, but the previous owner of my 1990 560SEC had installed a new wiring configuration to support more powerful headlights before I got the car. I found this out when I went to replace a bulb and discovered the more powerful bulb he had installed.

I would not have known the wiring had been changed, but was kind enough to respond to my inquiry as to why the bulb I found was more powerful than the Factory spec.. He told me he upgraded the wiring to avoid over powering the factory wiring (for want of a better description). Said he had wanted to avoid "outrunning the headlights"

Is it possible that this may be one factor contributing to your problem?

Lou Miller

PS Don't ask me what he did or how he did it. He works on satellites and deals with that sort of stuff all the time. I just turn the key and enjoy. 


----- Original Message ----- 
From: Dan Landiss 
To: Mercedes Coupes Mailing Lists
Cc: calvin young
Sent: 3/4/2011 10:50:37 AM 
Subject: Re: [W126 Coupe] dim passenger light


on 3/4/2011 6:14 AM calvin young wrote: 
Dan
Guys, 

I cannot think for the life of me what would be causing those odd voltages.

Steve is right. You have a bad ground somewhere. The negative voltage you reported earlier confirm that. The connection you had the black voltmeter lead clipped to at that exact time is the bad ground. When you then touched the red lead to a good ground, it read negative.


  I cannot see any relays in the lighting circuit

There are none.


I cannot imagine that the switch would be causing this.  Mice did get into the car at some point and perhaps they have shorted something out, but I have looked and could not find any chewed wires.  

If you had the same color wires on both sides somebody has already fiddled with the wiring. The alarm installer, perhaps?




Voltages are:

                left hand    right hand

white         12.50          0.23
yellow         0.53          5.50
brown         0.23           5.55

What we don't know is whether that was with the high beams or low beams turned on. Also, the 5.55 volts on the brown wire is the bad ground you are looking for. The brown wires should be zero. Where are you clipping the black lead from the voltmeter? Are you still seeing negative voltages at any of the connections?




voltages at the fuse seem to be correct.  They are:

F2 high beam right 14.01
F4 high beam left   14.02
F6 low beam right    0.53
F8 low beam left      0.56



That is also a sign of shaky grounds. the voltage at an "off" lamp should be zero, not over a half volt.


-- 

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