Blower motor fuse tripping, can't find problem

What is your question?

My blower motor fuse is blowing when the engine is running and the switch is turned on to any speed. It does not blow the fuse with the key just turned to the on position, it then works on all speeds. So far Ive tested the motor itself, it is good, replaced the relay, that wasn't it ( I tested it first and it seemed to be working but I put a new one in just to rule it out). I've also tried testing the fuse slot with a test bulb and did not get any voltage when there shouldn't be. I'm not sure what to do next, do I test the resistor or is that a non issue. I have the wiring diagram but that's not my forte so I need a little advice on what direction to go next. One thing i noticed and I don't know if it means anything is that the light behind the ac button (you depress it to turn on ac and it lights up) had been out for a while, but the ac button worked fine. After the fuse blew, when putting a new fuse in and turning the blower on, the light lit up again, and then of course the fuse blows and nothing works again. From reading i know there is a connection from switch to blower and the fuse panel to the instrument panel, i just am not knowledgable enough to know what to start testing next and what to rule out. Thanks! .