what voltage should I have at the coil

OK, just checking on the location of the tester. Did you clean the inside of the cap with a good clean rag? Button is good, right?

Try this: disconnect the - lead from the coil (disconnect the ECU from the coil). Take a short wire jumper and ground the - coil lead for a short moment with the ignition 'on', and then immediately unground this test lead, and see if you get a good spark out of the HT lead from the coil HT post; you are imitating a set of points this way. Don't be holding the wire lead when you remove it from ground; it might bite a bit. This will tell you if the coil is OK.