[Solved] 1989 300CE Tachometer/Clock/Oil Pressure problems
 

My 1989 300CE has non-functioning tachometer, clock when ignition is on, and oil pressure. I've replaced all the fuses in the fuse box with new ones, as a first step before taking the cluster out.

The first thing I tried was swapping a working cluster from my 1989 300E into the car to test and all the gauges started working. However, I smelled a burning smell and immediately pulled the cluster out. I put the 300E gauge back into its original location and thankfully it is still working. (edit: I think the oil pressure gauge is busted now. It is now pegged at 3 instead of fluctuating around)

I've taken both clusters apart trying to find any burnt traces that need to be reattached with a wire and I discovered this:

http://i.imgur.com/ZXVbc5Ql.jpg

Does anyone know what that trace is or what it does? It looks like the left turn signal ground wire if I'm not mistaken. Where does the trace go to? Will fixing this solve my problems with Oil/Tach/Clock ?

I would agree with your assessment, looks like the ground wire to me. I can't quite see underneath, it looks like it runs to a blue/green cylinder. Might be the ground connection on the device that runs the oil pressure gauge.

Without a ground connection the oil pressure gauge won't work, so, in theory restoring that would restore functionality. But why the trace blew up in the first place is the main question here. Thats a pretty lengthy bit of trace be all missing too.

I think the tach/clock pod can be powered up separately from the oil/fuel/vac gauge pod. I would try doing just that, power them up separately. I can't remember what the connectors look like though, you might need an alligator clip wire to provide ground for the clock. I seem to remember it having a single 12V connection. Might be the same case for the tach. It might have a two pin connector.

Wonder what caused all of this. Any alternator issues? Maybe voltage spiked? We have the OVP for protection but it does not protect everything. Its only hooked into a few key engine electronics units.

OK I believe I fixed this problem now. I was looking at the wiring diagram which tells me that the oil pressure gauge, fuel gauge, and water temp gauges should all be on the same ground.

http://i.imgur.com/cmBXN8k.png

However, upon checking this with the continuity meter, there was considerable resistance from the oil pressure gauge to the other 2 gauges (~340 ohms), but the water temp and fuel gauges passed the continuity check.

So I made this little wiring unit:

http://scontent-a-sjc.xx.fbcdn.net/h...02814561_n.jpg

And connected the 3 gauges together at the 7mm nuts

http://scontent-b-sjc.xx.fbcdn.net/h...93910869_n.jpg

I plugged everything back into the car and nervously turned the engine on, ready to yank the key and the cluster out immediately if anything happened. To my delight, everything began working again:

http://scontent-a-sjc.xx.fbcdn.net/h...58596400_n.jpg

Just a side note, I did swap out my tachometer for a known working unit as well, but I may not have needed to. At this point, I'm too lazy to swap my original tachometer back in to see if this wiring hack fixed the tachometer, so this is inconclusive.

I hope this helps someone else down the road.

I have almost the same symptoms except that my oil pressure gauge is working. Tach and clock are inoperable except that the clock works when the ignition is off.

I don't know if I'm looking for the same trace. Or the same fix - if these three items are tied together as it looks from your photos.

Do you have a map of the traces or is that included in the diagram you posted and I just don't know how to see it?

I assume I'm looking for a bad ground - just not sure what to look for within the cluster.

Thanks.

Edit: I find no trace of a fried trace. I am perplexed having checked all fuses. What got your clock going again properly?