what are the symptons of a bad coil on merc thunderbolt ignition?

I've never in my life had a coil go bad, though I convinced myself that it was several times, then after the new coild didin't fix it, I had to find the real problem.

I just swapped out the module, rotor, and cap on my TBIV, and it fixed the problem. I'm pretty sure it was the module. I bought the parts from Bam Marine, and got them in one day.

rough running,after a little bit coil gets hot sometimes after the motor will shut off, no spark

If in doubt, buy a $12 external resistor coil (GM) at any auto parts store. They work fine and are a lot cheaper than the Merc coil.

I lost my first coil last year. Motor started running really crappy then died. Pulled of the coil wire and was full of oil. Of all the spare parts I carry I didn't have a coil.