Low Voltage to the coil

That may be normal, depending.

You need to find out if the coil/ ballast COMBINATION you have is correct, that is, a heavier, hi - ratio coil will draw MORE current, and pull supply voltage DOWN through the ballast

The reason these are called "ballasts" is because they do change resistance with heat. It's "how they work."

A better test is to check the "key side" of the ballast. Better yet is to measure "harness voltage drop" directly

To do this, turn the key to "run" with engine OFF. Hook one meter probe to battery POS, and the other to the key side of the ballast (opposite from the coil side)

You are hoping for a VERY low reading the lower the better

Anything MORE than .3v (three tenths of a volt) means you need to look for a problem

Your top suspects are the bulkhead connector, the ignition switch connector, and the switch itself

The circuit path involved here is battery -- fuse link -- bulkhead connector -- ammeter circuit -- ignition switch connector -- through the switch -- back out the connector (dark blue, IGN run) -- back out the bulkhead connector -- to the "key" side of the ballast

When making this test, if you have breaker points ignition, make sure the points are closed.