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.