I was working on my old snowmobile today and went to check the spark and it only sparks on one of the coil wires. I tried switching plugs to see if one was bad but I'm pretty sure that the coil is bad. The coil was fine last time I was working on the snowmobile and it had great spark on both sides but now it has spark on just one side. I was wondering what are some possible causes other than just being old and wearing out that can make the coil go bad. Can a bad voltage regulator cause a coil to go out? I'm using the original voltage regulator in my 1980 jag 2000 body with the 1978 panther 5000 engine and everything worked great until i cook the engine and rebuilt it. Also when i had the original jag engine in it the coil went bad that was brand new and it only worked for a year after i had all new electical put on it.. cdi, internal and extrernal coils new.