So you are talking about the instrument cluster, right? To really help, readers will need to know the year of your car and of the donor car.

Beginning in 1983, 240s were pre-wired for the large tachometer. Look in there for a Red-White wire with an insulated terminal on it. That's the lead from the coil. It connects to the tach.

Cars with the large tach also have a small clock mounted in the uppermost of the 2x2 panels to the right of the instrument cluster. The clock is powered and lighted via a three-wire harness from the tach. Get that harness, and the only other thing left to do is to install a little plug to seal the hole where the clock adjusted was.

As to your other question, gotta know model years.

Good Luck,

Bob

:>)