Charger connection problem
 

Have my first cart,2005 TXT. When I bought the cart the guy there tried three chargers before he got one to come on and start charging. He took a little screwdiver and bent the little spring loaded piece of metal down inside the plug on the inside by one of the prong. Since bringing it home I have had trouble getting it to charge. Sometimes by wiggling it around it will click and start charging, but most times not.
I took the plug apart and one prong was loose, screw seemed to be stripped and wouldn't tighten. That prong has been hot at the back, insulation was lightly browned and the red wire in the middle has been hot. The plastic had melted alittle by the one prong.
Can I put a larger screw or a nut on the back side of the existing screw?
What is the smaller red wire in the middle for?
And how long should I leave a 12 volt charger on the two batteries to charge them? My charger can be set at 6 or 12 volts which would be best and 2 or 6 amps on 12 volts. Going hunting this weekend and have to have the cart charged!!

Thanks
Buford