I picked up a small tach which I'd like to install in my 93 240. The tach has some wires on the backside which were clipped off to remove it from the donor car. The top two are for the light....should one of them be grounded? The bottom 3 wires I'm not so sure about, other than they power the tach itself. What/where should these wires hook up to? In a question not to far below on this list, I asked about a red/white wire behind the instrument panel that isn't hooked up to anything. Is this wire part of the answer to my question? Oh, one more question: this little tach has lots of film on the backside of the dial glass. How does this thing open up so I can clean the backside of the glass? I tried turning the black bezel ring, but that's all it does..turn. Is the ring crimped on somehow so it can't be removed at all? Or should I use my bottle cap remover? ;-) Thanks for your wisdom!