Low voltage to coil

Measure the voltage on the other side (feed side) of ballast resistor. It should be about 12 v. If it is, your coil or ballast resistor could be bad. I am assuming you have a ballast resistor.

If it is a stock ignition ballast resistors and coils are pretty cheap. I would shotgun both.

If voltage is not near 12 v, more troubleshooting of supply circuit will be needed.