Gremlins! Demons! Jumping gauges! - PeachParts Mercedes-Benz Forum

seacoast_benz · #1 04-08-2004, 10:51 PM

'83 380SL here, with suddenly dark instrument panel at night. SO navigated her way home without gauges, and asked if I would take a look.

I expected to find burned-out illumination bulbs, and/or a played-out dimmer rheostat. Removed cluster per comments here, replaced bulbs, still no light. Shorted across the rheostat and, voila, well-lit panel. Since even the max setting is pretty dim on a 107 panel, I soldered the patch wire in place.

So far, so good. Reconnected everything, but inserted the cluster shallowly enough to remove it easily. Normal pattern of warning lights from pre-ignition key turn. I had also removed and adjusted the combination switch, because of an intermittent open circuit when switching between high and low beams. Tested that. A-OK.

Tested the right turn signal. Ruh-roh! It works, but the fuel gauge snaps back and forth between end stops while the turn signal is engaged. Likewise for the left turn. And the seat belt warning light dims as either TS flashes.

Ignition is normal and the engine runs properly. Tach responds as it should. However, when running, the temperature and oil pressure gauges behave as the gas gauge does, fluctuating in tempo with either turn signal.

Pretty sure that the reconnection was proper. All of the critical points use different connector heads, and they're keyed to avoid misaligned insertions. Sensible design.

I pulled the cluster again and opened it. No visible burnthroughs on the circuit traces. No apparent cracking of solder joints.

Bad ground? Pulled out the 107 service manual and checked the ETM. The instrument panel is supposed to ground to G102, "behind center of instrument cluster". Took a look there, but there aren't any wires visible that ground to vehicle structure. The only thing that suggests itself is where two middle-size wires are fastened together via ring terminals on a small plastic bracket. Unscrewed connection, cleaned, reassembled with a drop of electrical contact enhancer. No change.

Sketchy fuse? The instruments are apparently on fuse 13. Removed and inspected it. Seems fine, though all of the fuses are apparently original ones. No fuses are blown. Polished the contact surfaces on #13 and used contact enhancer. Again, no change.

The big round barrel connector that hooks up to the back of the cluster caught my eye. Internal short? I opened it. For those who haven't done this, do so only with great care. The only thing holding the individual wires in their slots is the connector shell itself. Once that's open, they tend to spring out. Without the diagrams in the ETM (themselves not great on detail) it would have been impossible to reassemble the thing correctly. Seems OK internally. Now that it's back together, the cluster behaves the same way as before.

I'm running out of easy ideas here! If there's anyone who might have been in the same barrel, I'd be indebted for any suggestion, however unusual.

txstinger · #2 04-09-2004, 05:47 AM

You probably found the first cause – Dimmer switch. Many times when removing the cluster (per board) it loosens the ground connection and is very hard to find. Many have run a new wire from cluster to chassis ground as the fix.

May fix your situation.

tan man · #3 04-09-2004, 08:17 AM

i also get dancing guages in the left instrument window only (economy, fuel level, oil pressure). movement is around 1/8" . it only happens with turn signals on. it did not happen 3 months ago and started happening after some engine work done.
recall some posts long ago with the fix, i'll run a search.
as for the results, some people love the added brightness bypassing the rheostat gives. others caution the long term browning of the bulbs, plastic and circuits. please let us know in a few months if you see any adverse effects.

seacoast_benz · #4 04-09-2004, 09:14 PM

OK, problem mostly solved. Appears to be an internal ground failure within the cluster. Will follow up later on with full details, but don't want anyone to waste time with further followups for now!

whunter · #5 02-02-2006, 06:09 PM

Quote:

Originally Posted by seacoast_benz

OK, problem mostly solved. Appears to be an internal ground failure within the cluster. Will follow up later on with full details, but don't want anyone to waste time with further followups for now!

Could you followup please.
Where did you find the DIY for cluster R&R?

sublettd · #6 02-04-2006, 10:42 PM

Sounds like the same problem I had a couple years ago...only I caused my own problem when I shorted out the ground on the instrument cluster. The fix was to run a new/separate ground from the post on the fuel or temp gauge to the frame. Mine is starting to 'blink' again so I probably need to tighten the connection again.

gireaud · #7 10-10-2006, 07:06 PM

Quote:

Originally Posted by tan man

i also get dancing guages in the left instrument window only (economy, fuel level, oil pressure). movement is around 1/8" . it only happens with turn signals on. it did not happen 3 months ago and started happening after some engine work done.
recall some posts long ago with the fix, i'll run a search.
as for the results, some people love the added brightness bypassing the rheostat gives. others caution the long term browning of the bulbs, plastic and circuits. please let us know in a few months if you see any adverse effects.

please let me know if you solve the problem, it happen to me too. thanks in advance.

Noeljb · #8 10-10-2006, 08:34 PM

Someone had this problem before and if I remember correctly the ground was through the speedo cable. He established a seperate ground and was up and running.

nobby · #9 10-13-2006, 04:26 AM

I never had a proiblem with the cluster but when I removed it to renew the bulbs I found an extra ground wire had been adde from the cluster to the chassis. Can't hurt. The only thing I changed was I added bullet connectors so I could remove the ground more easily.