Here's the dash on my '86 CVX 18, it should be the same as yours.
Hope this helps you.
Here is the back of the tach on my 1986 CVX 18.
Wire ID
Blue - dash light, goes to speedo light
Large Black - Ground from wire harness, goes to center terminal, common to other black wires
Gray- goes to ignition coil
Black 3- goes to black wires on temp guage
Purple- from wire harness, usually +12v when ign is on
Black 2- goes to black wires on speedo,