Cranks but won't start?

Bypass the ballast resistor. Run a wire from the battery positive terminal to the coil side of the ballast terminal. I suggest a 14 ga wire with alligator cilps at both ends. I made this and it's part of my tool box. If the car fires and runs then it's the ballast. Be aware that the motor will NOT shut off if you do this unless you disconnect the wire. And dont run it more than 1/2 hr. The ecu will get too hot and you will burn it up.

I actually have battery positive to a switch and then to coil + just in case the ballast pops on my M body. I run the FBO ign and MSD ballast and the FBO tends to run the ballast very hot. To help with poping ballasts I also spaced the ballast out from the fire wall about an inch by putting a nut on the back side of the ballast mounting bolt. This gives it a little better air circulation.

I also ran a ground wire directly from the neg battery terminal to the FBO ecu body..

I have also seen intermitant spart due to a cracked coil which had lost it's oil. Goddam accel garbage..

And yes,where are you measuring that voltage?