Quoted from KillerQ:
Thanks! Any guidance on a specific way to test the source? Or at least that the problem isn't the coil?
Look at the coil and see if there are signs of over heating or melting. Move the plunger by hand and see if the slingshot moves freely. (IF it does not, it locked on and you have board work and a coil to replace.) Make sure the playfield wires going to the coil haven't broken and inspect the tiny coil wires that connect to the lugs, too. Also, inspect the stand up switches behind the rubber aren't gapped too close (or too far!)
If that checks out, all the coils are individually fused under the playfield. There is a huge bank of fuses, find the one for the slingshot and test it with a multi meter. If its blown, swap in a new one (or grab one from the left slingshot ) and see what the coil does. If it energizes immediately you know you have board problems.