^ We'll have to disagree, I'd put it closer to 25% if that, depending on make/model.
Granted, there's a test for that. Normally the resistor module is bypassed for full fan speed so you can set it to full and see if it's making the airflow it should. If it's not, I would've replaced the blower before the resistor module blew, but if dealing with someone else's vehicle, they may have waited till it was a more complete failure.
It should never take the harness out unless we're talking about an insulation failure from age. That's why there's a fuse (not the one on the resistor module, rather the main fuse compartment fuse) , that should blow before that much current fries the wiring or connector, unless of course the connector was faulty in the first place, or someone swapped in a generic chinese fuse that doesn't blow at spec'd current. A lot can happen in 15 years, have to take each vehicle on a case by case basis.
I wouldn't replace anything else yet. Once the resistor is in, you can tell if it seems working properly. If it is overheating, the thermal fuse in it will work fine to cut power, it's a resettable fuse not a one-shot blown, so it will survive the test, but after a number of thermal cyclings over years, can fail open even if it doesn't reach its trip temperature. Seen it too many times from various things, automobiles to coffee makers, hair dryers, curling irons, space heaters, etc.