I was just at a junkyard and found a '82 300td with the tach/clock combo gauge. My '81 300td has just the large clock in that spot. How hard would it be to swap in the tach/clock? What do I need off the junkyard car besides just the gauge? Thx!

the tach amp

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What is that and where is it found on the car? What does it look like? Thank you...

I'm guessing you'd need the "pickup" at the front of the motor, the cable from that should plug into
the "diagnostic" socket at the left-hand side of the engine bay. You'll need the "impulse sender" which
plugs into that socket, likely the socket itself, and then the loom which goes to the tach.

That should be everything, but I could be missing a few things (or even entirely wrong:p)

edit-- Make sure you have a little "nub" on your balancing disk, I believe this is what the "pickup" needs to generate a signal to the impulse sender. Just compare it to the one you're taking the parts from.

this

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First you need to look at the donor car, follow the wires from the part pictured they should go to a terminal strip. 2 wires go on to the terminal block then to the pick up above top dead center on the fly wheel. It takes a tiny wrench to remove like 5,5 mm I think then off the same terminal block on the fire wall. Two other wires should go into the wiring harness that goes into the cabin if you don’t have these 2 wires your in for a lot of work and some soldering.
Dave San Jose CA.

Do some of our cars have a mechanical tach run off the back of the injection pump?

None of the 617s have that kind of IP. Maybe some of the older ones did.

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Thanks for the info. Very helpful. The motor is gone from this car so it looks like I won't be able to get everything I need off of it. But the tach has already been removed from the dash and looks in fine condition, so I might go ahead and take it and then work on acquiring the rest of the parts later. I'd really like to have a tach in my car!

Just checked my car and it turns out that it DOES have the tach pickup on the crank and the little nub on the balancer. So it looks like all I need is the wiring from the diagnostic plug to the firewall (and maybe on to the instrument panel). Thanks again!