Photo of, or a link to this "test light"?
If you're testing for spark, USE A "REAL" SPARK TESTER calibrated for HEI.
Nothing with a light-bulb is going to be appropriate, including junk sold as "spark testers", and timing lights. You need to
have the spark jump a calibrated gap, not fire some silly neon or fluorescent bulb.
www.amazon.com/dp/B003WZXAWK/?coliid=I3S98D7T1J0RLJ&colid=2VLYZKC3HBBDO&psc=1&ref_=list_c_wl_lv_ov_lig_dp_it
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As said, #3 seems to be a weak spot in the Vortec distributor cap. There's a frightful number of caps coming from Communist China, including crap with fancy, boutique names like MSD.
Correct. The ignition module (and the ignition coil) has no idea which cylinder is firing. IF (big IF) the cam sensor/crank sensor alignment is within spec, the computer knows. That's how the computer identifies a misfiring cylinder. So if the cam/crank sensor alignment isn't correct, the computer could be confused about which cylinder is the problem child.