Need Help from the Electrical Wizards - PeachParts Mercedes-Benz Forum

Tpawlik · #1 11-30-2010, 08:48 AM

I recently lost all the lights on my CCU, vents and shifter. Everything but the instrument panel lights. Jeremy sent me an N40 Illumination Contol part and a great picture of the wiring diagram. Unfortunately the new N40 did not fix the problem. I was so sure the part would solve the problem I did not test the wiring for power. If I am reading the wiring diagram correctly, terminal 30 gets power from the # 9 fuse, terminal 31 is the ground and power out is thru 58d and 58D. If I have 12V at 30, 58d and 58D, the problem must be downstream. What is X6 and X6/1?
If I do not have power at 30 can I put a jumper on that wire from a known 12V source to at least test the rest of the circuit? If I have power at 30, can I put a jumper on 31 to verify the ground?
I tried a continuity test on the N40 I removed and got nothing. Is the N40 a relay that would only show continuity when power is applied?

Jeremy5848 · #2 11-30-2010, 12:26 PM

I had a similar problem in which I had no power at pin 1 (circuit 30 = +12 Volts) of N40. I ended up installing a jumper from the wire that feeds power to the clock. That's how my car is now wired. Try jumping 12 Volts to that pin and see if the lights work. If so, then the N40 relay is good.

X6 is a connector buried forward of the ashtray and the airbag sensor. Access is not quite impossible, just almost.

To answer your specific questions,
(a) an ohmmeter test may not help for this component because it is solid-state (no relays). So I suppose I shouldn't call it a "relay," it's more of an "amplifier."
(b) you should be able to put +12 Volts on the gray/red wire attached to pin 2 of N40 and all of the console lights and such should light up. You can even use that as a permanent replacement although you won't be able to dim the lights.

Jeremy

pmckechnie · #3 11-30-2010, 12:37 PM

I am a little confused. The only car you have in your sig is an 87 300D. N40 in an 87 300D is the audio amp and has nothing to do with the dash lights. Your problem (if the above is the correct car) is probably the red fuse on the back of the instrument panel. X6 and X6/1 are just tie points to connect wire together. They are under the radio/ashtray area.

Paul

Jeremy5848 · #4 11-30-2010, 01:30 PM

Quote:

Originally Posted by pmckechnie

I am a little confused. The only car you have in your sig is an 87 300D. N40 in an 87 300D is the audio amp and has nothing to do with the dash lights. Your problem (if the above is the correct car) is probably the red fuse on the back of the instrument panel. X6 and X6/1 are just tie points to connect wire together. They are under the radio/ashtray area.

Paul

Sorry, can't agree. The schematic for the '87 300D (page 128) clearly shows N40 as the "Instrument Illumination Control Unit." The 1987 300D didn't have a separate amplifier; the radio is "A2." Additionally, the little red fuse that looks like a lamp socket until you remove and look at it was not installed in the 1987 instrument cluster. It didn't show up until 1989-90 or thereabouts.

Here is the schematic. N40 is marked in yellow. Please ignore the other scribbling, this pic was originally used for another purpose.

Jeremy

Tpawlik · #5 11-30-2010, 02:50 PM

Thanks guys. I will connect a jumper from the clock feed on the back of the instrument panel to #30 and will report back.

pmckechnie · #6 11-30-2010, 03:31 PM

Jeremy, you are correct, Alldata got me again. I went back and looked again and found 2 VERY different pages for the instrument lamps. There is not a day that goes by that we don't find atleast 1 error in Alldata. I just can't win.

Paul

Tpawlik · #7 12-02-2010, 07:16 AM

Ok. I have 12V at socket 30 and a good ground at 31. I plugged my N40 in and with the headlights on, tested 58d and 58D...no voltage. So I think I have confirmed my N40 is no good. I ran out of time to do the same test with the replacement N40, but since the wiring is providing voltage and it is does not work either I'm guessing it is also no good.