Replacing old tacho

[Diablo]

Hi guys,I have an Evinrude 1992 2stroke 120hp outboard I want to replace the existing tacho which is all weathered and in poor condition,the dial on the back is turned to 6 and is a OMC brand and was still working I just want to know what specs with a new one that I will need and something that will preferably connect to my existing wires,Hope someone can help Thanks.

[disorderly]

Diablo,
hope you dont get the same tachos as what are being fitted with E-tecs.
I'm waiting for another one to be fitted.This will be the third new one inside 12 months.

Scott