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  #1  
Old 03-22-2007, 04:29 AM
'84 300D Owner
 
Join Date: Oct 2006
Location: Dallas, TX
Posts: 210
electrical problems... long

I had two electrical problems that I recently fixed, and I want to keep them from happening again. I'm pretty sure they were related, and I have a solution in mind. Here's what was wrong: my console lights were always on. If the key was in run or start, the lights were burning. The headlight switch had no control over them whatsoever. The strange thing was when the back left power window was moving up, all the console lights would go off. I found the problem in the left rear door jam. The wires had long ago been pinched and stripped and spliced. It all made sense to me. In run or start, each power window switch has a wire that goes hot, and the hot wire in the left rear door jam had spliced with the wire that powers the LED in each power window switch. So the circuit was completed to ground through the string of lights that go behind the CCU and the fiber optic spider. The power was just flowing in the opposite direction. Hence the "always on" console lights. The dimmer switch in the instrument cluster is also connected to the console lights and window switch lights and is supposed to be the source of the power. I think this is why I had two burned traces on the circuit board of my instument guages. I think the backflow of electricity caused a short and burned the traces. Is this possible?

These two problems are fixed, but I want to know how I can prevent the electricity from flowing backwards to the instrument cluster, should the rear door jams decide to pinch and splice my wires again. Would wiring in a diode be a viable solution?
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'84 300D
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  #2  
Old 03-22-2007, 05:16 AM
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Join Date: Mar 2005
Location: SoCal
Posts: 650
I put a 1 amp fuse between the grey blue wire and solid blue wires. These wires are located in the center panel(Close to where your right knee would be if you were driving). Mine was intermittent but the lights would only come on when you have the keys in park or start, not when it is off. Thanks for the tip. Ive been troubleshootng this problem for a while.
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'85 300D Cal 280,000 miles
'07 C230 37,000 miles
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  #3  
Old 03-22-2007, 05:44 AM
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Join Date: Nov 2004
Location: Nova Scotia, Canada.
Posts: 6,510
The diode sounds worth a try but you have a voltage drop of about 1/2 volt across it when it is conducting. You might try it for all the effort and cost it takes.It will do no damage.
I might measure the current to size the amperage requirement of the diode first though. I have not really thought it through to see if there are any other implications .

Last edited by barry123400; 03-22-2007 at 05:52 AM.
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