Combination switch problem

Hi everyone I have a 2002 tacoma that I bought aND replaced the engine anyways I have a problem with the headlight, turn signal combination switch. I had this problem for 3 switches now I bought them from autoz one when I turn my head lights on the high beam indicator lights up and all the parking/rinning lights come on. The headlights how ever doint. If I lurn the brights on the lights com on. I had this problem so I replaced the switch and worked great then abut three weeks later anout 4 weeks and then it started doing the same thing again, so I replaced the switch again and worked good. Now about 4 weeks later I am having the same problem and the last time I replaced it I noticed 5 the plug that plugs into the switch the harness looks like it is melted a little bit and I am having a hard time finding the harness plug anyone have any suggestions??