[geetee50]

Hello i have a 15hp 1989 mercury, i've no spark on my bottom cylinder, it starts but runs rough, i've tried the coil on the top cylinders green/yellow supply wire and the coil sends a spark, the compression is 120 on both cylinders, could it then be the switch box? Would any one have some advice please on other options or what to test.

[Kev144]

Ill give ya some advice that I learned the hardway when i was new to outboards (still kinda am). I had a problem with mine not idling. Did some tests and was weak from the switch boxes. I replaced those and same problem. Turned out to be a stator and something i should have checked in the first place as the source then if that checked out, my next option would be the boxes. Just a FYI anyhow to you.

[lots of boats]

Hi
Switch boxes seem to just quit, no middle ground. Sometimes when you disconnect and reconnect things you solve the bad connection problem, two simple places to suspect are the ground from the coil, and the high tension lead connection inside the spark plug cap. Try all the little things first.

Cheers

[kellyisu]

You should do an ohm reading on both the switchbox and the stator to save you money and time. Good place to start your troubleshooting.