get an alligator clip jumper and connect the hot wire on the working side to the hot-wire on the non-working side. Now hit the switch on the working side and both should fire. If so, the coil is good. Then hit the switch on the non-working side. If none fire, then the problem is the wire to the non-working coil. Check the connector off the board (if it's solid state) and the drive transistor for that coil.
If the non-working coil does not fire with the hot wires jumpered and hitting the working side switch (and the working side coil fires), then switch your jumper to the ground wires to the coils. if it works now, then your problem is with the ground connection to the coil. if it doesn't then the coil (or the diode on it) is bad...