does your shift light have a spot where you can plug something in to?

if not you need:

RPM Activated Switch
The MSD RPM Activated Switch can be used in a variety of applications where a device needs to be activated at a specific RPM point. By supplying a ground to devices such as solenoids, lights, beepers and retard devices the RPM Activated Switch can be programmed to activate the functions of these devices at any RPM. The switch can be programmed for 4, 6 or 8-cylinder applications. The RPM point at which the activation occurs is easily adjusted using the same RPM plug-in modules that are used on the MC-2 Ignition. No RPM modules are supplied with the unit and must be ordered separately. See below for a complete listing of RPM Modules available.
RPM Activated Switch - PN 8950




your shift light will have 3 wires and the switch will have 5

light will have power ground and signal
switch should have power, ground, signal in and two signal out
one signal out (yellow and grey)

obviously power and ground go to uhh power and ground
on the light signal goes to the signal out on the switch
signal in on the switch goes to distributor.

there are different configurations but for lighting a shift light you're going to use the yellow wire signal out wire.

good luck.