Re: 1979 85 hp Evinrude electrical problems
kimcrwbr1 is right. I like to use spray battery cleaner on the battery positive and ground terminals. After they are cleaned and reinstalled I give them a shot of battery protector spray. I also use it on all ground terminals where they touch the engine. You can get it at any autoparts store. If your key switch is accessible under the dash disconnect the battery and remove, clean and reinstall each wire. Wipe a finger full of battery protector on each terminal before reinstalling. Look for corrosion where the wire feeds into the terminals. I have had to remove the old terminals due to corrosion, (label the wires first) strip the wire back, coat w/solder paste, retin the clean bare copper wire w/solder and a soldering gun then install a new connector. With the wires off you can check the switch w/an ohmmeter.
Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.