The blower has a voltage dropping array for various speeds. I think it is under the hood. Check for voltages there with the blower switch on. I do not know if it is on the high or low side of the blower motor.

Even more important is to pay attention to the blower fuse connections etc. This circuits fuse holder is famous for being of marginal design for the current it handles. Since the blower stopped working before you changed the brushes it probably has nothing to do with what you have done anyways. Take your meter and check carefully around that fuse holder area.