The MSD I had (actually two different ones) it wasn't the light, the timing actually was all over. One time it would run all right, next time it'd just about blow the starter drive off, or be so retarded it wouldn't run. You could feel it changing as you went up the road, the sound would change at random, and so would the power. The last one is still on the firewall, impresses the hell out of gullible school kids but doesn't do anything.