this is a long, confusing story.. but i need help!!

so..... i made a pain in the *** mistake and reversed the jumper cables on the car i was jumping my van with while i was in a hurry (yeah... it ended up slowing me down. now i will ONLY ever use a battery pack to jump my cars. hindsight...) i caught it before i started any of the cars BUT still managed to melt off the positive terminal from my van, other car left my error without a scratch.
i replaced both of the terminals, charged my dead battery, put in a new starter (which was basically the whole reason this happened.. my laziness & a bad starter) and went on my 2 hour drive home. didn't notice anything wrong minus a slightly higher temp gauge (it was very hot out that day) and drove it probably 3 times after that original drive without noticing issues other than a the temp gauge being higher than usual. one day i was driving on a busy road and looked down at my gauge to see it literally as far beyond H as possible so i freaked out, pulled over and popped the hood (because i didn't notice any extreme heat coming from under the hood) and checked the most obvious reasons why my gauge would be that high without my car exploding, such as fan belt and coolant levels. after searching and searching, while parked in a mcdonalds parking lot, i called my dad, who said maybe it was a thermostat issue, and then i called a nearby garage. while driving it there, maybe 2 miles down the road with many stop lights along the way, i stalled any time i had to stop at a light, which had never happened to me before. when i got there they looked at it, said "yep thermostat" replaced it and $175 later i was driving home.. BUT i made it maybe less than a half a mile down the road and the gauge shot directly up past H. so i called AAA, got a tow back to the garage (i was too afraid and frusturated to drive it at this point) where the mechanic and i went for a ride and noticed this very very strange thing.... while my van is in drive anything that draws power causes the gauge to go up. this includes; break lights, radio, headlights, heater/air, cig lighter, interior lights. also, while the van is running the interior lights are surging slightly and the inside left blinker light stays lit (the one on the dash, not outside). SO WEIRD. we looked around.. didn't see anything obvious, decided it can't hurt too much to drive it and i headed home so i wouldn't be late for work.
the last week or so i have been ripping apart my dash and under the hood looking at all of the wires to see if any have melted and are causing shorts. haven't seen anything. now i'm going to buy a tester for my fuses (which are the old tube type) to see if those got messed up and i still need to check more of the grounds for some wires.
does anyone have any insight into this issue?

sorry for the long story. it's just a weird one with lots of factors... and i'm new to this mechanic thing since buying my van a little over a year ago and doing most of the work myself (with the help of my mechanic dad and uncle) so i can learn but this electric stuff is way over my head.

 

Sounds like you melted a ground strap. There should be a solid bond between the battery negative, the body, and the engine block. The loss of any of these grounds can cause voltage to seek another path, such as through sensors.