If the heat mats are gonna be next to each other, running as one then I wouldn't bother cutting the cables. I'd just put a double adapter onto the stat and plug them both onto that. There's no chance of an overheat then either.
What size are they at the moment? and out of curiosity, why do you need a larger one?
awww yes i forgot the double pin plug never mind yes there right next to each other i have not got £20 to spend at mo and need heat mat asap so i joint 2 small ones i had lying about :) thx for the reply kehhlyr
this doesn't always work,tried it my self the other week with 2 identical mat and temps were always out.if 1 cools quicker than the other,when they come back on one will have a head start,was a major head ache.