Intermittent electrical loss at motor

I was cruising down the lake at full throttle and suddenly the motor lost all electrical power. The tilt/trim wouldn't work either. This is on a Carolina skiff with a 2014 Yamaha F70 4-stroke. The gages worked, and showed I had 13v on the battery. I took the cowling off and checked the fuses and wires to the starter/ect.; Nothing was loose. Tried the ignition and it worked. Shut it off, put the cowling back on and it was dead again. I repeated this process several times and made up new dictionary curse words. Finally was so dumbfounded with it that we drove back to the ramp with the cowling off. Then, to add insult to injury, when I had it back on the trailer I put the cowling on and tried the trim/tilt and it worked just fine. Ran it with earmuffs back in my driveway both with the cowling and without, poking around and wiggling every visible wire and connection but I couldn't reproduce the problem!
Any ideas on what to focus my investigation on? Many thanks in advance!

Start at the battery connections and move forward from there, especially the grounds.

Intermittent faults are always wiring related. Sand all grounds metal to metal. Clean all connectors with electrical cleaner and put back together with dielectric grease. I like to do a few connectors at a time so you have an idea where the fault was.