I have my 12v pump in a battery box. I bought a 4” 12v fan from radio shack and wired it into the same switch as my pump. It worked for a couple minutes then it stopped working. I returned it to radio shack for another one. i installed it and wired it the same and got the same result. Am i supposed to have a relay or something? Is there a fan alittle more heavy duty that I should use? Any input is much appreciated,