Alternator started sparking

Well there are about 5 answers to this, none of which are right or wrong. "It's up to you." You surely must have learned the system somewhat by now, and have some idea what you are doing, and what "is not" wrong

You can fix what you have

But a used harness and either use/ repair it or use parts of it to repair yours

Buy a new "repop harness

Or buy an aftermarket "universal" harness and start over

So far as MSD, if you have not, go to their website and paw around. Somewhere in the MSD sit/ destructions are some troubleshooting tips. Things like you can use the white breaker points wire to trigger the box to check it, etc. Make sure the white is NOT grounded.

I would "hot" wire the MSD to check it. Always suspect the distributor connector Make sure it has ground (big black) and that big red and small red are hooked to battery. Disconnect dist, and ground/ unground white to check for spark. Then check dist pickup connections and dist. itself