Well Im not too familiar with our wiper motors, but since it is in essance an eletric motor, it should generate some heat but if it's very hot to the touch, then something is wrong. The motor might be completely fried. If the wiring follows normal wiring convention, the green should be the ground red is usually pos and black neg or common. My guess (I would look it up 1st before you try any of this, I know there is somewhere with a wiring diagram online, Im at work atm so I cant look it up) is that the green is chassie ground, red positive terminal or to wiper switch, black neg terminal or another part of the switch. Im guessing (this is pretty much a shot in the dark) that since the switch is "varible" its probally 3 resistors in parallel and when it is pulled out it makes contact with one of the 3, there for limiting the voltage to the motor, thus causing different "speeds". If you have access to a varible DC powers supply I would connect the green to a ground then red to pos terminal, black to neg and slowy increase the voltage up to a max of say 10V (just for testing purposes)I would clean off all contacts as it might not be making a good connect/ground resulting in improper voltage causing excessive heat. Now was the sound a "clunk" or a pop? Clunk would probally denote something mechanical either braking within the motor make causing a short also a source of heat, vs a pop is electrical, atleast from my experience. Hope this "shotgun" post helps in some manner and hopefully someone more knowledgeable will reply as well. Good Luck
-Alan

EDIT: After looking at the diagram link I posted below, disguard my idea on the green wire, all 3 of them go to the switch...green goes to the "P" terinal, black on the "A" and red on the "F", that is if your wiring is stock. One lead from the P on the switch should go to the 25Amp fuse on the block (no1 according to diagram....hope this helps