Multi-function Relay Buzzing (plus dead instruments) - PeachParts Mercedes-Benz Forum

bustedbenz · #1 05-10-2009, 01:57 AM

Alright. i've got something odd going on. I was making a long trip the other day, with passengers, no less, when every gauge on the dashboard went to zero. (Except the clock) - fuel, OP, temp, speedo, and tach all were unresponsive. They stayed that way for the rest of my run to the airport (and back home). When I got home and started checking, the multifunction relay (black box in the fuse box, containing three individual relays) was buzzing and vibrating... one of the three was oscillating as fast as it could, and presumably had been for hours.

So here's my complete list of observations. Any other suggestions besides "the relay needs replacing" or should I just say "it's fried" and replace it?

1) When the relay is buzzing, everything seems to work normally anyway.

2) It's definitely the turn signal components that are malfunctioning. When I signal a turn, left OR right, the buzzing stops and the relay functions normally. As soon as I cancel the signal, the buzz returns.

2b) The lights are NOT visibly glowing while the buzzing is occurring. They may be oscillating so fast I can't see the glow, but if they are doing anything, I can't prove it.

3) Removing the #7 fuse to the turn signals also stops the buzzing.

4) I HAVE observed instruments functioning simultaneous with the buzzing sound, but it's been rare.

5) When the instruments are not registering anything, the row of warning lights (low oil, low coolant, etc) ALSO refuses to glow, even during the self-test with the switch on but the engine stopped.

6) SOMETIMES, I can remove fuse 7, and then reinstall it. When I do so (while the thing is on and buzzing) the buzzing stops. The instruments are working. Then, I'll drive down the driveway, flipping signals on and off, and very frequently (sometimes it takes longer than others) as I trigger a signal, the gauges will drop and when i get out I discover the relay buzzing again.

So... what's my trouble? Is the relay fried? Or is there a problem in the turn signals themselves causing that oscillation instead of a problem with the relay itself?

That relay has NOTHING to do with the instrument cluster that I can determine. So why are the gauges all dying?

Jeremy5848 · #2 05-10-2009, 12:43 PM

What is the part number? I have a used spare, may be the same thing, part number is 201 821 00 47. Runs the turn signals/hazards, w/wipers, heated rear window. Much cheaper than a new one from the dealer, let me know if you're interested. Guaranteed, $30 shipped in USA.

Jeremy

bustedbenz · #3 05-10-2009, 07:45 PM

It's the same part, but I figured it out.

The ENTIRE symptom list was cured by replacing the #6 fuse, which had a hairline crack that evaded my observation until tonight.

pdrayton · #4 01-11-2012, 09:50 AM

WOW! Thanks for that post bustedBenz!

I've had the same problem for weeks, even went so far as to replace the relay, and remove the access panels in the dash to check for shorts - no dice.

After reading your post I went out and checked fuse 6 - it wasn't seated correctly. Reseated it, and there is no buzzing and the gauges move! Hopefully it stays that way.

Paul

bustedbenz · #5 01-11-2012, 10:12 AM

Quote:

Originally Posted by pdrayton

WOW! Thanks for that post bustedBenz!

I've had the same problem for weeks, even went so far as to replace the relay, and remove the access panels in the dash to check for shorts - no dice.

After reading your post I went out and checked fuse 6 - it wasn't seated correctly. Reseated it, and there is no buzzing and the gauges move! Hopefully it stays that way.

Paul

Glad I could help. I had completely forgotten about ever having this issue.

This is why one of those "How to use the forum" things includes the advice to always post how you fixed things for posterity.