I don't have a multimeter or anything fancy, just my eyeballs. The last bunch of blank carts I bought have the black wire running directly into the little white center tube, instead of sitting nestled in the cotton. It's making a burned-wire smell, clogging the entire cart, and making the draw a strenuous affair.
I phoned support and after making me feel insignificant, the guy grudgingly agreed to send me some blue-colored ones, which, I hoped, would work as well as the blue ones I'd bought before. Same problem again.
I don't think these guys believe me, meaning they haven't tested the things themselves. This is a problem, and it may be dangerous. It'd be really cool if someone from Vapor4Life would email and straighten this out. I only have 5 carts left from the good old days, and a whole bunch of worthless defective product. This weekend I'll be seeking a new supplier if it isn't settled but quick.