I have a 1974 70 HP evinrude that will not start or fire. Last fall we sunk the boat, we got the boat back up and let the motor dry. The motor then fired right up. It ran for about 15 minutes and then died and has not fired or started since. We changed all the plugs. Just need some ideas of where to start at now.
The first thing I would do is find a manual for the motor. It will help alot with the wiring and different items. It will also have alot of different things to check and a order to do them so you can find the bad part. With some motors you have power packs of different type and it will show how to check them also.
Unfortunately, I also have experience with sinking a motor. I found my distributor completely full of water. Assuming that you've already ruled out something obvious like that, I would recommend that you start at the key and work back. If the key is sending power to the motor, check for power at the points. Slip a piece of 400 grit sandpaper into the points and slide it back out. This will make sure they don't have crud preventing electrical contact. If the motor doesn't have points, test for continuity on the magnetic trigger wires. As the previous post suggests, a manual will walk you through all of this!Good Luck!