Dead Dials

[Zagato]

During a hot afternoon in traffic, the instrument panel suddenly failed. The indicators stopped working (yet hazards work), the rev counter stopped working, the temperature gauge stopped working, and the fuel gauge is giving inaccurate readings. The only dials that work is the Speedometer and Oil Pressure.

As for the indicator stalk, high beam and flasher works. But still no action of the indicators. The battery light works, but when I engage the parking brake, the light for that doesn't come on and causes the fuel gauge to drop off to zero. Added to that, movement of the indicator stalk makes the fuel gauge needle flutter.

Any ideas on what the problem is? I really really hope it's just a grounding problem, but it doesn't explain the failure of the other instruments.

[Big_Richard]

the speedo and the oil pressure are mechanical gauges, so thats why they still work The oil pressure gauge has a plastic tube going to it straight from an oil gallery in the engine, and the speedo is driven from a bowden cable from the extension housing of the transmission.

Your miriad of instrument faults will all be in common and have a single fault, possibly either a disconnected ground connection or blown fuse. I would suspect the ground connection first since the tacho is just pulse driven straight off the coil, and the pulse is obviously still there, because the engine is still running

I would pull out the cluster and have a look for any loose connections too

[Zagato]

I checked the fuse box, no blown fuses. So that leaves a grounding fault or a connection that came loose.
(Don't know if this has anything to do with it, but the temp gauge was last reading 200'F before trouble started)

Do all the electrics have a common ground, or does the instrument panel have its own, which I must search for?
Is there a proper way to pull out the cluster? When I try to remove it, it stops just before it's out, as something without much slack is attached to it.

Also, I've discovered the brake and parking brake pedals affect the fuel gauge reading. 'Half' when not applied, 'empty' when applied.

[TJ 450]

Is there a proper way to pull out the cluster? When I try to remove it, it stops just before it's out, as something without much slack is attached to it.

Also, I've discovered the brake and parking brake pedals affect the fuel gauge reading. 'Half' when not applied, 'empty' when applied.

That sounds like a bad ground connection for sure.

To remove the instrument cluster, you may have to remove the steering wheel, remembering to mark its position on the shaft. The speedo cable is probably preventing it moving out any further, which is undone by hand (there's a knurled fitting screwed on to the rear of it).

There are some ground connections just behind the instrument cluster, but you should probably study the wiring diagram in the library section of this site, to determine which is which.

Tim

[Big_Richard]

also be careful not to snap the oil pressure tube, they are no longer available new and they are quite easy to dammage. It will require a spanner to undo its connection, 10mm from memory.

(DONT START/RUN THE ENGINE WITH THIS DISCONNECTED!!!)

[timinoz]

Did you ever get this fixed? I have exactly the same issue with my 280SE.

[marku]

Yes take great care of the oil gauge connection I sheared mine off and then found that they were no longer available. If the union is rusted to the bush, as mine was, I would cut the pipe off at the union and subsequently refit it, there is just about enough free pipe to do this. I can't get the indicators to work. Everything seems OK the hazard flashers work but not the indicators I am hoping it is not the steering column switch.

[oscar]

When some of my dials stopped working I found it was due to dodgy earth connections but I'm pretty sure the indicators were still ok.  I can't remember.  Anyhow, regarding the earth connection, this may help you fellas, marku and timinoz.  The earth comes in via one of the wires in the round multipin connector behind the oil/fuel/temp tripple gauge.  It travels along the back of the cluster via contact between the PCB of the male side connection of the multipin connector to the backing plate of the speedo/odo gauge, then via contact between that backing plate and the plate behind the clock/tacho gauge.  The long screws that force the backing plates together as they hold the gauges in the cluster may work loose or the plastic threads in the cluster become threaded which might cause poor earths at any of those points and/or the solder joins in the PCB for the multipin connector may have poor or loosened solder joins.  The problem may extend further up the line though, particularly the earth supply to the multipin connector.  Simply test with a cheap test light, probe on earth connection in the connector and positive lead clipped onto clock supply which will always have 12V supplied to it regardless if ignition is on or not.

I fixed my poor earth by supplying a run-around wire soldered to the PCB on one end and soldered to the clock/tacho back plate on the other.  Earth supply to the multipin connector was never a problem though. A couple of pics:
The first pic shows the shim with the extra blob of solder on it, which would normally transfer earth to the speedo/odo backing plate by contact alone.  That blob of solder holds a thin grey wire which is visble in
the second pic, sodlered to the back of the clock/tacho plate.



I'm still a bit iffy about the hazards working but not individual signal lights when activated.  Though I'd guess it's earth related so far as the hazard circuit might have a separate earth supply to that of the turn signal combo switch circuit?  But I don't know.

[Casey]

I'm still a bit iffy about the hazards working but not individual signal lights when activated.  Though I'd guess it's earth related so far as the hazard circuit might have a separate earth supply to that of the turn signal combo switch circuit?  But I don't know.

That's exactly what happens when you've got a wiring/fuse issue.  Hazards always work for some reason.  In my SEL I was running without a fuse box cover for a while and the gauges would work okay, but as soon as I'd try to turn on a signal, they would all go dead and the signal would not work.  After a few minutes, the gauges would come back, but die again as soon as I hit the turn signal stalk.  I wiggled fuses around (none were bad) and applied some dielectric grease and replaced the fuse box lid and all was well.