Batteries or Battery Holder overheating

Hi Guys, I purchased another buggy, and it was pretty much brand new, only had 1 tank through it. It didn't come with servo's or an on off switch or battery holder, which was no problems.

It is a bump start hyper 8, I purchased a 2 new battery holders and 2 on off swtiches, obviously 1 to use of each and 1 spare. I also had another holder and switch from another buggy which works fine.

After installing the new switch and battery holder it doesn't light up the receiver which to me would indicate no power, but after 5 or so seconds it the batteries are heating up the holder and it gets extremely hot and starts to smoke and melt the battery holder. I used the other new one on my other hyper 8.5 and it powers it up fine. So I then put it in the new buggy again the same overheating problem happens. I have also used the other spare holder and switch from my other buggy, again it powers up my 8.5 with no problem, buy when I put it in the new buggy again the overheating problem with no power and then the holder starts smoking and would melt if I left it turned on.

What would cause this? Has anyone had this happen and how did you fix it?

Thanks In Advance, Mal