87 300D heater control illumination stoped working - PeachParts Mercedes-Benz Forum

davidlee · #1 05-14-2013, 06:14 PM

All the lights went out on my heater control panel all of a sudden, is it one bulb that lights it all up, or is the problem on a circuit board somewhere? All of the other night illumination in the car is working fine.

SORRY DIDNT MEAN TO POST 2X

Jeremy5848 · #2 05-14-2013, 06:28 PM

The PBU has two bulbs, usually covered with black tape. You'll need a piece of tubing (shrink tubing works well) to reach in and extract the bulbs. I agree it is unusual for both bulbs to go at once but that is the first thing to check.

There's a picture in the following link (first of three pictures). You can see the two pieces of tape that cover the holes where the bulbs are.

Jeremy

http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/244053-w124-climate-control-unit-ccu-sale.html (The unit has been sold but the pictures survive.)

davidlee · #3 05-14-2013, 06:42 PM

Thanks, I will check that first, plus I dont know what farther to do.

jay_bob · #4 05-14-2013, 07:06 PM

Power for the CCU bulbs comes directly off the rheostat (i.e. not through N40). It comes from the X6 distribution block behind the console, then to X1:14 (the left hand PBU connector, pin 14) and then on to the illumination pin for the recirculation switch.

If the recirculation switch lights up at night then chances are the illumination power feed to the PBU is good.

Need a wiring diagram, go to www.w124-zone.com and register, they have a cleaner copy than what is available on M-B's own site.

pwogaman · #5 05-14-2013, 11:26 PM

My 87 300TD (mfg early 86) and BodhiBenz1987's 87 300D (unk mfg date) both have the N40 feeding the X-6/1. That booster circuit then feeds the lights for the climate control, window switches, seat heater switches, fader, power mirror, gear select indicator, and several, but not all, of the switches on the panel above the climate control.

On both our cars the power failed on the items leading from the X-6/1, and on both our cars the problem turned out to be a short in the wiring leading to the rear window switch on the rear door panel at the door hinge. We both initially believed the problem was the N40 itself and tried swapping it out without success. My problem only occurred when the rear door was closed, so when trouble shooting I recommend opening and closing the rear doors.

You can check for a short reaching to the X-6/1 cluster by checking for strong continuity between the N40 socket at #2 and ground.

She fixed hers by removing paneling and pulling the wires back and then resoldiering. I fixed my by slicing in extra wires from a donor car and then pushing the two slices back in "B" pillar and the door respectively so that the donor wire was now at the hinge. I also used shrink wrap. I you do, just be sure to put it over the excess wire slack prior to soldiering the second splice of each line. Then slide the shrink wrap over the soldiered joint and heat.

Both of our N40s worked after making the repair, leading me to believe that it must have some built in reset type of protection. We both now have extra N40s. Incidentally, per the MB configuration drawings, the later W126s omitted the N40 and simply put a jumper between socket #2 & #4.

Here are some pictures of my repair:

jay_bob · #6 05-15-2013, 08:50 PM

I had to do that on my 300TD as well. Same exact problem.

According to the ETM, the CCU lights are on the X6 block, which is before the N40 (wiring code 58d). Not to be confused with X6/1 which is after the N40 (wiring code 58D).

BodhiBenz1987 · #7 05-15-2013, 09:10 PM

Quote:

Originally Posted by pwogaman

My 87 300TD (mfg early 86) and Bondi-Benz's 87 300D (unk mfg date) both have the N40 feeding the X-6/1. That booster circuit then feeds the lights for the climate control, window switches, seat heater switches, fader, power mirror, gear select indicator, and several, but not all, of the switches on the panel above the climate control.

Mine's manufacture date is Dec. 1986. I believe that is the setup on all U.S. 87s (i.e., cars with power windows and/or seat heaters) but I could be wrong. However, I think Jay_bob is right about the cc control button lighting not coming from N40 ... mine still worked despite the short in the circuit from N40. I think those two bulbs, the hazard switch and the air recirculation switch are straight from the rheostat. The stuff on N40 should be: dome light switch, antenna switch, rear headrest switch, all window switches, mirror switch, fader, shiftgate and two of the vent control switches (left and right, I think). The wiring to the rear window switch illumination was the culprit of my problems, just like Paul's. It took me forever to figure this out as I spent a great amount of time dissecting the console area and not even thinking about the back door (even though I was simultaneously trying to get that rear window working ... only worked in certain door positions ... should have been a big clue!).
DavidLee, when you say all of the lights went out, do you just mean the fan speed, temp dial and cc setting buttons, or everything on the cc panel? If you've still got lighting on the top buttons (dome light switch etc.) and shiftgate/window switches/etc., it is probably just individual burned out bulbs. It's possible they both burned out at the same time, especially if they were last replaced at the same time. They are a pain to remove ... I used a drinking straw with super glue on the tip, stuck it over the bulb, let it dry, then pulled right out.