Just read your reply to TvMan and RoyB.
The wiring on the breakaway should not matter. The plastic pin basically separates the two wires from each other and it you pull the pin the wires touch making a connection.
On second thought to my post above. It is possible that you have wired the breakaway wrong. If the wire from your battery positive terminal to the breakaway has any splices in it, you would be feeding 12v from the splice to the trailer brakes and bypassing around the pin in the breakaway. The emergency breakaway should use a single fused dedicated wire from the battery to the switch.