heater 30A fuse keeps blowing on 90 ranger

[sharpertouch]

went to turn heat on for the first time in a long while. motor started to spin and blow air. then 20 seconds later i heard the fuse pop. a couple days later i got around to swapping in a new fuse. popped immediately when ignition was turned on. turned control knob to off and put new fuse in. turned ignition on and no pop immediately. but 10 seconds later after turning control knob on she popped.
another new fuse and control knob off and ignition off and she does not pop until i turn ignition on.
installed NEW blower motor.
another new fuse and control knob off and ignition off and she does not pop until i turn ignition on.
i unpluged the new blower motor i installed and yet still she pops.
any suggestions?

 

[RobbieD]

another new fuse and control knob off and ignition off and she does not pop until i turn ignition on.
installed NEW blower motor.
another new fuse and control knob off and ignition off and she does not pop until i turn ignition on.
i unpluged the new blower motor i installed and yet still she pops.
any suggestions?

That makes it sound like the problem may likely be between ignition switch and the blower switch. Look at the blower switch next. Over time they can get a little crispy and melty (it may even be obvious visually when you pull it out to look at it). Once you've pulled the HVAC control out away from the dash, unplug the blower switch- then if you lose the fuse popping when the key goes on, bad blower switch. If it still blows, you've got a short in the wiring back to the ignition switch (just make sure the blower switch connector ain't melted inside itself, causing the short). Good luck.