the car an 83 300d t. tach was malfunctioning. did the search on rubber bands/cigarette butts etc. but when i actually open the hood and looked around i discovered that the wire to the 'tach' cylinder on the inside left fender was not attached to the engine. continued the search and found only the following cryptic reference "In mercedes a connection to the oil pump drive is used" (to power the tach?). my question where does the tach lead attach to the engine? also the square crossection attachment to engine end is covered in some type of epoxy. my epoxy has been somewhat abraided revealing the copper windings. second question. do i have to replace this wire given that i can see the windings? thank you.

I'd be interested in a full explaination of what makes the tach. work. Mine is in pieces since the butt and solder fixes didnt work.

__________________
Paul
2004 E500 4matic; 72,000mi

Have read the tach threads for some time. My tach pegs at 6000+ as soon as the key is on. Nothing seems to affect that.
Is that what goes on with the rest of these? Or is this a bit out of the usual problem. PO told me he had replaced that black part on the fender well. Looks to be new, and the cig butt does not affect anything.

I believe that the wire that you are refering to is the one that attaches to a fixture at the front crankshaft pully. It gets a magnetic signal from the pully.

I've also tried the "traditional' tach fixes on my '83 300D T, but to no avail. Like Flybob, I traced the tach cable to the flywheel. There does appear to be a feature of the cranshaft pulley that creates inductances every time it cycles past the sensor at the end of the tach cable. This allows the RPM's to be counted. My sensor was totally gummed-up with oil and other diesel crud. I cleaned it with WD-40, but still had an intermittment tach. I'm now thinking that over time, the heat of the engine has aged the wires sensing the rotation of the pulley. I'm getting intermittment connection somewhere.

Another strange thing with my tach is that is works when I run the heat in my car whenever "something" kicks on every few minutes to circulate coolant (my guess). I think my problem is mostly electrical do to this phenomena. Any thoughts would be appreciated!