'85 300D cluster troubles
 

1985 300D 123.133

While removing the instrument cluster, I managed to let the 12V spade terminal (that attaches to the tach) dance across the rear of the cluster. The few sparks that followed managed to blow the interior lamp fuse, no big deal.

The oil, temp and fuel level gauge now bounce around like flippers on a pinball machine, the tach will not function and all warning lamps including hazards glow dimmly.

What the **** did I do? Kicked myself in the butt first then thought about how to go about repairing my **** up. I traced the problem down to the oil, temp and fuel level assembly. As best as I can tell, there are three resistors soldered to the board, two out of the three are open. Does anyone know the value of these resistors?

For now I am using the old gauge assembly from my 240D leftover parts box, it only has one resistor. It was used with the plastic fuel tank assembly, so the fuel gague is a few clicks off. At least the tach and gauges are back to normal.

Alan

That wire going to the tach, is the 12v for the clock. i think there should be a cover on the end of the spade. but what ever.

I have a different gauge combo Iam using, one with oil pressure and the F temp range. it is out of a 79 123 240 or 300D or older. mine works good w/o any problems.

You have access to any PNP yards? if so, just pull a gauge out of a later 123, or the whole cluster for around $35. each gauge is around $16.

This coming weekend is 50% off.

probably should disconnect the battery when messing with the wires. I have done what you did w/o any problems,..................... yet :rolleyes:

Charlie

The thing that throws me off is that the oil gauge flutters... It is a mechanical gauge, not sure how it would be effected.

Do note that the 85 uses a three-pin tach, whereas the older cars use a two-pin version. I have an 85 tach (never verified that it worked) that you could try if you verify an issue.

I did once cause a short on a gong and blew out a trace on my cluster on my 91 BMW. Was an annoyance to fix. As I recall, the w123 has three separate sections, so something to determine is if there are PCBs that could have acted like a "fuse", or if you just blew out the different electrical gauges.

Don't throw it out!

You most likely burned out the ground on the PCB cluster. Just run a new ground wire to the collection of grounds behind the insulation and that will fix the issue. Attach the wire to the screw that connects the metal speedo to the three gauge cluster.

If you cannot figure out the value of the resistors, take them out and go to your local Radio Shack and compare them. Or ask the guy at the counter. They should be able to help

I have been wanting to pay a visit to a Pick and Pay yard for eons now, the closest one to me is a few hours east..........
8219 Mechanicsville Turnpike
Mechanicsville, VA 23111-1216
(804) 559-7390

The way the cluster was lighting up and needles flipping back and forth looked like the time someone slipped a purple microdot into a Coca Cola I was sipping on at the time without my knowledge. It did not hit until driving down Route 64 east of Charlottesville. Stuff was flying out of cars that did not exist. So I must have been having a flashback regarding the oil pressure gauge.

Thanks for the correction regarding the 12V connector, the tach uses a three pin connector. Don't know what I was thinking about. I'm sure there are others that will agree with that statement.
I am not throwing away the gauge assembly, and will look adding a new ground as mentioned in a reply. I did check the grounds behind the cluster, gave them a good cleaning.

For now everything is working with the 240D gauge assembly. I appreciate the offer from JHZR2 to try a different tach.

I'll pay a visit to the local Radio Shack.