You can throw parts at it until you give up or run out of money.

Or you can do some troubleshooting.

A coil needs only two things to spark, voltage and ground. Once both are hooked up the coil charges up, remove either and it will produce a spark. The factory setup removes the ground to spark the coil

You are either missing the voltage at the coil, or the ground is either always missing or always present.

You can use a spark plug int he coil wire to see if it has spark, you can use a test light to see if there is voltage to the coil +, light should be on if the key is in run or start. You can use a test light on the coil -, it should flash as the engine is cranked over. Any of those conditions fail the test that is where you problems area is.