Hey all, i bought a sunpro super tach 2 for my cavalier, only to find out that hey they claim it needs a stupid adapter. They're wrong.
There's a resistor inside it on the 4 cylinder channel, it registers 390 ohm, the cavalier requires double that or close to it to get a proper reading.
I put a 1Megaohm pot in where the 390 ohm resistor was, and adjusted it to double, and bamo fully adjustable and tuneable tach.
I will try to get a hold of an autometer and experiment with it as well, since thoes damm tach adapters are 100 bucks, and the resistor mod is um i dunno 50 cents at your local electronics shop.