Javy:

The max should ever have is 12 v. The heat was generated by a short -- low resistance, high current, high heat.

You should have popped a fuse before the coil burned. Your tach filter repair sounds like the problem source.

Melting some of the rubber backplane doesn't sound good. Your are better off slicing with an Exacto knife or fine grit grind with Dremel. tool to expose the connector without heat. If the backplane is multilayer, it can be messed up with with excess heat.

Sorry, in a former life I was Micro-Miniture Electronic Repair Certified.....