right now I have two subs hooked up to one mono amp. The amp has 2 pos. and 2 neg. posts so each wire coming from the sub has its own post to go too. I plan on upgrading to 3 subs using the same amp, where should the wires go from the 3rd one? should i just put them in the same spot as one of the other subs? this is probably a very stupid question but I wanted to make sure before I did it.