thers 2 easy ways.
1) on my stock coil it has a + and a - mark, you want to tap into the groud side (-) it is the side that is switched and provides a signal
2) use a dvom and unplug the coil. probe the connector and find which wire has 12V when the key is in the on position dont use this wire use the one that reads 0V
The other wires should be wired up one pos one neg and some have seperate wires for a light, for the light tap into the wire for the bulbs in the inst cluster
Josh