I have with me 4 wires: a black wire, a red/blue wire, a white wire, and a red/white wire.

These are the wires that are on the small tach?

The tach needs (1) signal from coil - red/white wire. Look behind the instrument cluster for a red-white wire with an insulated female connector. Many 240s are pre-wired for a tach.

(2) Ground - black wire. Needed for both light and signal to work. Ground to a nearby bolt.

(3) power for the light - either red-blue or white, I don't know. There are brown wires to many lights in the center control panel that feed the lights from the dimmer switch.

Good Luck,

Bob

:>)