Electrical Gremlin diagnosis - E320 Wagon courtesy lamps - PeachParts Mercedes-Benz Forum

cphilip · #1 01-27-2009, 10:48 AM

Car is E320 wagon 1995. Appears new engine harness. No other problems what so ever outside of the power headrests need to be re-clipped and are loose from the rods. No other items not working as they should. Perfect in every way except...

Problem is with the four Courtesy lamps in the rear pillars. Two in B pillars and two in rear most pillars. They go off and on sporadically with no real clue as to why. No consistent fix as far as opening and closing doors or locking and unlocking. Will come on magically and then go out after a while.

One other clue. When they are on they appear to not be fully energized. By that I mean if I moved the three way rocker switch to full "On" they appear to glow a tad brighter. But they do not often respond to the full "Off" position when they have come on by themselves.

Work to diagnose so far is that I removed the three way rocker switch from the switch array in the dash. At that point it appeared fixed as they were not coming on at all. Checked this three way rocker switch out with ohm Meter and it appeared fine but I left it out until I could try a new one.

Now.... fast forward to this morning.... a week and three days later... go out to get the paper and they are on. Car has been sitting for three days without any use. Was run for a week after removal of the switch with no sign of these courtesy lamps coming on that I saw. But this morning for some reason they are on all by themselves. They were not on at 11PM and have not been on any other time as I have been watching it carefully.

No reaction from them to locking and unlocking. No reaction to them opening and closing doors. Finally insert key into ignition and turn to position 2 and they go off when key is turned back to off. And stay off. An hour later still off.

Start car and they come on but then go off as soon as car is cranked and stay off all the way to work. And after shutting down they are still off.

They must take power feed from some other direction than the three way switch... or.... at least they ARE getting power from some other direction. Not sure why. Logic tells me they should run completely through the switch but maybe not? Perhaps there is a back feed from something else that has been seen before? Something running in contact with one of the door switches?

I can always, and temporarily will, do the Click and Clack fix and that is to remove the bulbs. But I would like to start thinking about fixing these if I can as its the only gremlin so far in the car.

lkchris · #2 01-27-2009, 11:01 AM

Now you need a new tailgate wiring harness.

They all break up at the hinge point eventually.

babymog · #3 01-27-2009, 11:06 AM

Just for fun, try unplugging the security system box under the passenger carpet. I believe that the '94/'95 combine the door light switch and the alarm switch, just a hunch.

cphilip · #4 01-27-2009, 11:55 AM

Good ideas....

But... another possible clue...

While I was taking out the four bulbs, the last one I got to... the one in the passengers side rear pillar, I found a wire disconnected. A Brown with Grey stripe was completely off it post. I did not go back and reinstall the bulbs yet to test this. But... how and why could that initiate a voltage through there is now got me wondering. Before I got back and test (because its is so sporadic there is no good quick test). It could just be a red herring but it is something out of place.

Got any ideas of if that could somehow cause it?

cphilip · #5 01-27-2009, 12:01 PM

Quote:

Originally Posted by lkchris

Now you need a new tailgate wiring harness.

They all break up at the hinge point eventually.

I guess I can examine it somehow?

I do note that all the wires attached to the various lamps were fine. No signs of deterioration. Just that one that was off when I removed the housing. It may have been off or barely on and came off with no effort. Not sure. But it was completely off when I saw it.

Will run these down then move to that security system if nothing prevails. Either way I have to reinstall the bulbs when I get done checking.

lkchris · #6 01-28-2009, 10:32 AM

Quote:

Originally Posted by cphilip

I guess I can examine it somehow?

It's the driver-side harness into the tailgate.

Visually inspect and feel it to check for broken wires inside. You can of course cut open the outside sleeve for a better look.

cphilip · #7 03-19-2009, 10:29 PM

Long time no see this thread.

I finally got around to this and I think I fixed it. At least it looks like it for now. And since the fix was not something we all had expected, I figured it best to report it in case it might just help someone down the line.

My Indy and some of his Pal up at MB Atlanta all felt it was coming from the overhead lamp over the Rear view mirror. You know that whole switch assembly and map lamp that holds the Sun Roof switch, Lamps and the temp sensor and all that? Well that thing. It is pretty expensive OEM part at about $125.

But it seems there is a timer in there in that main Lamp plug that does affect all the rear courtesy lamps too.

So taking their advice I put a new on in and it now appears that was it. In fact I never knew there were Seat belt warning flashers in that thing which now work. I had no idea they were supposed to be there so I never suspected that part.

And all the lamps now seem to be behaving normal. So far. I will give it a day or two to be sure. And report back if not but they are, so far, acting normal as they should. All of them.