I would like to know what it means? I am new to the I/O I have a '96 Merc 350 V8, I didn't winterize my boat(temp didn't go below o degrees,mild winter) Motor was running until I changed the oil, it turns over but won't start. I know the block isn't cracked, I checked. My I/O is in a '96 Ciera Express 22 ft. The gas is good I emptied out old and put in fresh. Gas is coming thru fine, I checked filter, the kill switch is on, changed spark plugs. What about the plug wires? How often should it be replaced? Thanks in advance! 