2010 mariner will start after sitting in sun on hot days but none of the electronics work for a few minutes, windows won't work, radio won't work, car won't go into gear???

I don't know exactly how hot you are talking here but a closed up vehicle gets very,very hot in the sun and I'd guess that that extreme heat is affecting some circuit. Sounds weird but maybe leave a window open a crack, find some shade and get one of those fold up screen things you see in car front windows sometimes. I always wondered why people had those giant paper sun glasses in the front window.

NE Ohio, both times the temp was in the high 70's to low 80's. Car sat all day in the sun. Dealer has no clue. Like I said, the car will start but nothing will work, no horn, no lights, no windows, no radio, no a/c, and it won't go into gear. It is like the whole car is fried. After a few minutes, everything is fine! Very weird. Anybody else experience this???

I read a few articles on tests done on the effect of sun on a closed car, results showed the air temp rising upwards of 130 degrees and the dash-board getting as hot as 190. Your dash has a lot of electronics. Put those temps together with humidity and you have a sauna. Would you be surprised if your digital watch acted a bit off after being in a sauna for 8 hours. It is obvious that your problem is related to the heat/humidity because everything works after the interior cools a tad. Now car manufacturers do a pretty good job trying to build cars to withstand extreme conditions but some circuit in your's is acting up. Stay out of the sun or pay a electronics tech $100/hour to test every possible circuit and determine which 50 cent piece of wire is screwing up in the heat!