Well, maybe try to manually trigger the event? This will tell you if the amplifier is still working. If it is shorted, the coils will spark at power-off just as if they were being fired.
The collector of the transistor will go to the amplifier and the emitter to ground. When the transistor is ON, the coil is charged by the amp like when the points are closed: when going OFF, it triggers the spark. So, find the wire that is connected to the transistor collector, touch it to the emitter-side circuit, then release it. When releasing, it should make a coil spark. If you have good eyes and tiny fingers, you might be able to do this right at the transistor on the points plate: just jumper collector-emitter, then open the jumper.
Obviously, on the Fours there are two of these...usually these systems have 3 wires to the points plate unless it also carries its own ground reference, in which case there may be a fourth wire for that.
