You should only have three connections, right? I don't remember the colors, but under the seat, one (#1) should be ground all the time, one (#2) should be +12V on low and grounded on high, and the last (#3) should be +12V on high and not connected to anything on low. So, assuming your elements are each 2 wires, you should connect #1 and #3 to one element, and #2 and #3 to the other (both elements share #3). This puts the elements in parallel on high, and in series on low.