Tach stopped on '82 300D--any ideas
 

My recently acquired 300D with 255K miles is running great, but the tach just stopped working this weekend. The only work I did this weekend was to replace the stereo so I am wondering if I could have done anything with that.
Where should I check to test the signal, ie. where does the signal come from at the engine, and what type of output should I be getting.


Thanks.

if you search the words tach and cig butt then you'll finds tons of answer :) Anyway,

I didn't use a cig. butt, I used a cognac bottle cork.

There is this thing that looks like a cylinder on the driver's side under the hood, just above the wheel wells. It's a small black cylinder with a screw on cap. Unscrew the cap and you should see that inside the cap there is a bunch of male connectors and the cylinder that is on the wheel wells has a bunch of female connectors.

Now, Just stuff the cig. butt in between the cap and the cylinder and tighten it down.

The other thing I did was to use WD40 in the holes... and amazingly it has not failed. I don't know if it's due to the cork or the WD40.

I tried the "butt method" but it did not work very long. Others have had better luck. I took mine out and completely resoldered it. It is potted so it's a bit of a chore to do.

It's been working for 2 or 3 months now.

Joe

PS there is a pickup down by the balancer. I believe it generates a small signal from the magnetic effect and feeds to the cylinder shaped item described earlier. I don't have a schematic and didn't put a scope on it so I don't know what signal levels we are talking about. I've been told that the sensor almost never fails... it's usually a bad solder connection in the cylinder.