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Old 07-13-2003, 09:33 PM
Registered User
Join Date: Mar 2003
Location: Grand Rapids, MI
Posts: 10
CD Changer bus line

W124 E420 1995
CD Changer/Becker Radio (1492)/pre-installed CD line problem ("cd line")

Summary of problem: my pre-installed cd line (from the radio to the trunk) will not operate an otherwise operational CD changer because the cd line does not have the 12 volt charge at pin no. 5 of the 10 pin plug.

Cursory answer/question: If the simple answer is order a new cd line and install it, does the cd line operate any other equipment between the radio and trunk? I doubt it, but that possibility exists. Further, I would like to avoid installing a new line from the dash all the way to the trunk.

Synopsis of testing conducted:
We had two W124 E420s to conduct our tests (Mine--non working CD changer, and Willy's--with a fully operational CD changer)

--Mine would not operate either CD changer. Willy's would operate both. Thus the CD changer was not the problem.

--My radio in Willy's car would operate both CD changers, thus my radio was not the problem.

--Thus, the only different item remaining was the CD line.

--With a multimeter, we checked for voltage on each the pins of the trunk plug when the line was plugged into the "C" plug on the back of the radio for both my cd line and Willy's cd line.
Willy's line/pins My line/pins
no. 1 = 0 volts no. 1 = 4.5 volts
no. 2 = 0 volts no. 2 = 4.5 volts
no. 3 = 0 volts no. 3 = 4.5 volts
no. 4 = 12 volts no. 4 = 12 volts
no. 5 = 12 volts no. 5 = 0 volts
no. 6 = 0 volts no. 6 = 12 volts
no. 7 = 12 volts no. 7 = 12 volts
no. 8 = 0 volts no. 8 = 0 volts
no. 9 = 0 volts no. 9 = 0 volts
no. 10= no pin no. 10 = no pin

As noted above, while Willy's line had 12 volts at the no. 5 pin, mine had 0. And, for some reason, my line had 12 volts at the no. 6 pin, while Willy's had 0. Plus, the 4.5 volts at pins 1 thru 3 makes no sense!

With my line, is there some way to just switch the line from no. 6 to no. 5? The color coded lines leads me to believe that this cannot be done.

Otherwise, any ideas to fix this situation?
Thanks in advance.

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Old 07-14-2003, 01:20 AM
La Jolla Audio
Join Date: Dec 2001
Location: San Diego California
Posts: 996
The problem can be in your radio and an easy is to pull your radio out and test your harness there or swap radios with your friend.

The Mercedes Specialists Since 1986
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Old 07-14-2003, 02:03 AM
wjm's Avatar
wjm wjm is offline
Join Date: Dec 2000
Location: Suburban Detroit, MI
Posts: 692

We did test test putting my radio in his car as well. It would not recognize the CD player. Again, his radio worked fine in my car with BOTH CD players.

I'm almost SURE it's a wiring problem of some sort.

We tested for continuity on all pins on both cars (some wires don't run straight through, though). Both outcomes were the same. The only thing different was the voltage outputs. I guess for grins we should have compared voltage outputs in both cars USING THE SAME RADIO. ... oh well. But again, his radio will work the CD player fine in my car.

What would REALLY HELP is a schematic of the CD input and the radio's CD output. Any chance you have this? With that (and if necessary), we could just run a new set of wires from the radio to the CD player.

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Old 05-17-2010, 05:09 PM
Registered User
Join Date: Apr 2002
Location: westchester, ny
Posts: 747
What was the outcome - I think I have the same problem, as my becker head unit reads CD M E even though two cd changers have magazines in them and neither works because the input voltage is not 12 volts (closer to .15 mv).

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