I acquired a freebie, 1983 K10, 305, SM465/NP208. When I got it, it wouldn't start, so I checked for spark at the plugs, there wasn't any. I put in a used coil I had laying around, and it fired right up. I thought, great! No money required! I put maybe 100 miles on it or so, and one day it stalled, and wouldn't start. Again, I checked for spark at the plug, and there wasn't any. Well, it was an unknown condition used coil I had thrown in there, so I thought that maybe it just failed because it was old. So, I bought a new one, threw it in, and the truck fired right up. I thought, great! She's good to go! That coil didn't last an afternoon, and there is no spark at the plug, so I know the coil went bad. Now I realize that something is causing the coils to fail. I checked the 'BAT' wire to the distributor cap, the wire is live when the key is on, and dead when the key is off, so I know the coil isn't energized when the truck is not in use. I tried looking at the wiring, from the fuse block down to the starter, and I see no obvious signs of damage. The fusible link wire to the distributor cap looked fine. There is a braided ground strap that runs from the firewall to the rear of the passenger side cylinder head, and another black ground wire from that point that seems to disappear into the wiring harness. That wire had cracked insulation, and there was quite a bit of green corrosion damage at that point. I went ahead and repaired that part of the wiring, but I'm not so sure that was the real problem anyway. Can a bad ground cause the coil to fail? I know the current has to complete a circuit. What about excessive voltage, like maybe the alternator is putting out too many volts (I did check it, it was 14.5-15 volts), but maybe it is spiking? I don't want to throw a third coil on there, not knowing how long it will last, and not being able to trust the truck. What causes a coil to fail?