Who can help here with RPM guage, anyone?

[rbort]

OK, I got this rpm guage for my 190E, mine didn't have it.
I put it into the instrument cluster and hooked it up to what I thought is right. It has three connections:

+
TD
Ground

I hooked up + to a live 12volt when ignition is on (coil + side).
I hooked up TD to the - terminal of the coil.
Ground is hooked up with the instrument cluster itself.

I start the engine, while starting the RPM guage hovers around 300 rpms (seems normal) but when the engine starts it jumps to 2k rpms. It bounces around there but if I rev the engine once it gets to 2k rpms and faster it works fine (like on the highway).

My problem is that it doesn't indicate correct rpms below 2000 rpms. My first thought is that the rpm guage is bad. So I went back to the junk yard and picked up another one but the second one behaves exactly the same as the first one.

Now for the big question: How do you wire this thing to work properly? Does it need a capacitor or resistor or something to make it work, or did I wire it in the wrong place?

Can anyone please help?!!

Thanks,

-=>Raja.