2 spark plugs go bad in 1 day?

Hey guys, me and my dad are working on his 1976 KZ400 and i had kind of a weird thing happen today. when i first pulled the bike out and started messing with it, i cleaned the spark plugs off. Cylinder 1 was black and fowled. Cylinder 2 was damn near clean. I wire brushed them both off and blew them out with compressed air. After re-installing them and figuring out where a few loose wires went under the seat, i decided to give it a kick with my KZ1000 battery hooked up to see what would happen. The bike ran awesome. Snap the throttle open and the motor would drop straight back down to idle. Everything seemed solid. Today i figured i would put on all the fiberglass bodywork that came with the bike to make it look better. I figured after i was done i would start the bike and make sure it ran good so everything ended on a good note I gave it a kick and it barely started... one i got it running it revved up really slowly and just ran crappy. Then it was all topped off with a carb backfire and it dying. So, like a dummy, i grabbed the header from cylinder 1 (assuming it was the one that wasnt firing since the plug was fowled) and burned the living hell out of my hand :silly:
I then spit on cylinder 2's pipe and found it was cold.
so i did a spark check on that plug and found it was grounding out inside the plug and intermittently sparking like it was supposed to. I hade a B8ES plug that was new just laying around so i threw it in there. Gave it a kick and it ran like it was ready to go anywhere. Later on today i figured i would make a youtube video of the bike to post on here just for fun.
While holding the camera, gave it a kick and it started running like poop again.. This time cylinder 1's pipe was cold and cylinder 2 was hot as hell.
I did a spark test on cylinder 1 and that plug was doing the same thing. This time i had an old plug that came out of my 1000 (but was still good) that i put in there. Now it runs awesome again. The wiring on this bike has always been kinda funny... is it possible to burn up a spark plug? Also, my right turn signal is always on like its on the Flash filament of the bulb and it wont come off. Must have been a problem before we got it too since the bulb melted through the blinker lense on the front and back signals. I already put in a known good flasher relay too. still no change.

Tried a different brand of sparkplug? I've had more than a few NGK's either fail right out of the box, or sometime later. If you can get the ones made in Japan, their probably good, it's the U.S. ones that seem to quit.

www.gadgetjq.com/spark_plug_cross_reference_motorcycle.htm