Use a bulb-type test lamp (not a voltmeter or LED) to check for power between the Red/White and Black wire terminals at the coil. If it doesn't light or lights dimly, check from Red/White to battery negative. If that lights brightly then the ground wire is bad, if it doesn't then the power wire is bad. In either case check the wires at the coil, it's not uncommon for them to fatigue and break inside the insulation after repeated removals. Also take a look at the female terminals, make sure they aren't corroded or broken. If you don't find any power problem, with the engine running, put a voltmeter on the remaining wire (it will be a different color for each coil) and compare the reading with a coil that is firing at the same RPM. The readings should be about equal, if they aren't then the signal wire is bad or the driver in the ECM has a problem. If they are equal then the coil should be firing, so you probably have a problem with the connector pins.