Replace the clock on the instrument cluster with a tach/clock combo. If
you are lucky you can find this at a parts yard or somesuch. If you are
even luckier, you can also find the wiring harness with the plug for the
tach, and the sensor which bolts to the engine. You need the plug and
the sensor. If you can pull the wires from the donor car, do it,
otherwise, with permission, cut them. Then you can run your own wire
through the firewall and hook it up. Wiring diagram of the car is a
REALLY GOOD THING to have.
(Who just scrounged the wiring harness for her 240D - 300turbo
The sensor is a little bolt on beastie that mounts below the vacuum pump
on the 300 engine. Don't know if they ever put one on the 240, so a 300
is probably your best bet for a donor. Get the mounting bracket as
well, since you will need that. Follow the wiring to a box mounted on
the fender, you need that as well. It is what actually counts the RPM.
The magnetic sensor just sends the info to the box. If you can find
wires leading past that point, follow them as far back as you can. They
will go into a large bundle. Unless you feel like teasing them out of
this bundle, cut them at this point. Then go into the passenger
compartment and remove the instrument cluster. If it is in good shape,
get the whole thing, since they are hard to find in cgood condition.
Note which plug goes to the back of the tach, follow it as far as you
can and clip it.
When you install, you can run your own wires through the firewall at any
convenient place. AFAIK, it should be a pretty straightforward job. I
have not had the time to put mine in yet, was cleaning up another car to
sell, but it's on the list.
One note: If you are getting parts from a salvage yard, GET PERMISSION
to cut wires before you do. Most places are pretty reasonable about it.
Especially as you are only clipping ones you will be taking with you.
Please, don't just go hackinng at things someone else might need.
This can get you kicked out of yards and this is NOT a good thing. I've
run into the results of people doing hack jobs to get at what they want,
never mind that they are destroying a perfectly good part to get to it.
They are invaluable resources for those of us with cars old enough to
vote and drink <G>.
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