Doc here,
imp:
To test the coil, you can OHM it out.
Set your DVOM to R X 1 , Ohms, calibrated 000, and first measure the primary side. It should read less than an OHM, but more than 000. More or less than that, toss it , it's bad.
Next, measure the secondary side, Set your DVOM scale to R X 10 K or higher, your readings should be between 10,000 and 11,000. Outside of that range, toss it, it's bad.
For a GM HEI in cap type coil, the proceedure is the same, BUT the Numbers for secondary are 6,000 to 30,000 Ohms.
This test will show functionality of the coil, but will not show Internal Arc~over due to winding insulating paint or Thermal malfunction. You need an Oscilloscope and a test jig, or running vehicle to determine that.
To "Spark" test it, get a 12 volt source, hook 12 VDC to the + side of the coil, Ground the coil to a bench vise, as well as your 12 volt source.
Install a plug wire in the Coil tower, and an old spark plug, and tighten it down in the bench vise where you can monitor the gap.
Hook a wire from to the - side of the coil and quickly touch it to the vise. The plug Should fire a nice BLUE spark each time you do this.
If it does not, OR the fire is anemic yellow or white, the coil is bad.
You will not be able to do this with a GM HEI in cap coil though.
Doc
imp: