[W124] strange bulb failures

[moose patton]

You have a case of the dreaded  VD!!!!!!!!  don't worry  it's not what you think, It's voltage drop.

If you find the headlight junction blocks ( where the headlights plug in) be hind the headlight assy's and check the voltage readings.  

Fro mthere i would check the lighting module, located under the fuses in the fuse box.  You will need the wiring manual to do a diagnostic on the wiring to tel you which wire goes where.

Jeff

92 50E,  92 300CE, 73 240Z

"Gibbons, Paul" <Paul.Gibbons at uk.thalesgroup.com> wrote:       @font-face {  font-family: PMingLiU; } @font-face {  font-family: Cambria Math; } @font-face {  font-family: Calibri; } @font-face {  font-family: @PMingLiU; } @page Section1 {size: 612.0pt 792.0pt; margin: 72.0pt 72.0pt 72.0pt 72.0pt; } P.MsoNormal {  FONT-SIZE: 10pt; MARGIN: 0cm 0cm 0pt; FONT-FAMILY: "Calibri","sans-serif" } LI.MsoNormal {  FONT-SIZE: 10pt; MARGIN: 0cm 0cm 0pt; FONT-FAMILY: "Calibri","sans-serif" } DIV.MsoNormal {  FONT-SIZE: 10pt; MARGIN: 0cm 0cm 0pt; FONT-FAMILY: "Calibri","sans-serif" } A:link {  COLOR: blue; TEXT-DECORATION: underline; mso-style-priority: 99 } SPAN.MsoHyperlink {  COLOR: blue; TEXT-DECORATION: underline; mso-style-priority: 99 } A:visited {  COLOR: purple; TEXT-DECORATION: underline; mso-style-priority: 99 } SPAN.MsoHyperlinkFollowed {  COLOR: purple; TEXT-DECORATION: underline; mso-style-priority: 99 } SPAN.EmailStyle17 {  FONT-WEIGHT: normal; COLOR: windowtext;
 FONT-STYLE: normal; FONT-FAMILY: "Calibri","sans-serif"; mso-style-type: personal-compose } .MsoChpDefault {  mso-style-type: export-only } DIV.Section1 {  page: Section1 }             Frank,
  
 If  you've got 6-9 volts without the bulb and 0v when you plug it in, you've got a  high resistance somewhere between the 12v source and the positive contact on the  bulb.  (assuming the earths are ok)
  
 I  think Mr Ohm had something to say about this....
  
  I don't know where the Light Control unit is, but if the other  side bulb is ok, the circuit supplying it is probably ok  too. 
  
 I  would start from the positive contact in the bulb holder and work back as  far as you can with a DVM or similar monitoring the voltage. The most  likely high resistance areas are connectors, so unmate/mate these a few  times and check for good clean contacts as you do. 
  
 If  there's a problem, you'll see the voltage change as you disturb  it..
  
 Good  Luck.  
    -----Original Message-----
From:    w124list-bounces at mbcoupes.com [mailto:w124list-bounces at mbcoupes.com]On    Behalf Of Frank Smyth
Sent: 17 July 2008 21:26
To:    w124list at mbcoupes.com
Subject: [W124] strange bulb    failures


      Hi folks
    
   Where abouts is the 'Lights control unit' located in the    W124 ? 
    
   I have an odd issue with one of the front fog lamps right    now - don't know if US cars have these, but they are the inboard lamps in the    front lamp units. Anyway, one is getting a healthy 12V, the other shows    between 6 and 9 volts - upon plugging a good bulb the voltage goes down to    zero. It's as if any load on the circuit brings it down. Bulb-failure    warning is lit up the whole time. The earths there are sound, I tested it with    a new earth lead to a test bulb; the cabling is sound too. Problem is not the    bulb, I have swapped in known-good bulbs
    
   I need to trace things back to the 'lights control unit'.    Fuses are good too - the number-4 fuse servers front fogs as well as the    single rear fog.
    
   Cheers 
    
   Frank
   Dublin, Ireland
   1992 230CE W124


   
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