I hooked my light from the points/coil wire on the distributor to negative to read when that wire is powered, and I'm finding that power comes on when the piston is around TDC. Shouldn't power be shutting off . Spark occurs when the points open. So your test light should come on when the points open. Look elsewhere.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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