I have a 25 HP 2002 Merc SN 0T557192 Mod 1025201ZD I have lost power and motor runs rough. I remove the lower spark wire and there is no noticeable difference in how the motor runs. Also, the top plug gets warm quickly and the lower barely gets warm. I have an excellent spark from both plugs/wires but lower cylinder does not seem to be firing. I have swapped coils and plugs but the same problem persists. I am thinking my switch box may be bad and is timing the spark incorrectly. Part number on the switch box is 855713-A2 but I can only find the A3 (Non-Commercial) and the A4 (Commercial/Jet 20) on this site. All help is greatly appreciated!
Thanks ahead for your help, Dave

Thanks ahead for your help, Dave