What is the difference in the wiring for a 3 speed motor and a 4 speed motor? I'm having trouble with the reconnection of the new motor.

What is this motor used for? How many wires did the old motor have and what were the colors... how many in the new motor and what are the colors.

I’m not sure I can answer your question but I will give you a possibility. I am working on a gas furnace. It’s wiring diagram is on the door. It shows wiring for a 3 speed blower motor. It shows a white neutral wire and then black, blue and red hot wires. The black is for high speed, the blue is for medium speed and red is for low speed.
However, the motor that is currently in the furnace has different wiring. It has a white neutral wire and then black, yellow, orange and red wires. Based on one piece I read and how the last HVAC repair man had the thing wired I would say that the black is for high speed, the yellow is medium, the orange is medium-low and the red is low. I’ll be giving a try tomorrow.

You should have gotten a diagram with the motor, or at least wherever you bought it should be able give you the info. Was it sold as a 4 sped motor? If not, it may have been meant to select many different speeds allowing you to adjust its speed to your system to give the best temperature rise. Doing so is a little tricky, you need to measure the incoming and outgoing temperatures. The furnace may give the proper temperature rise in a decal somewhere.

Just put a wire nut and electrical tape on the unused wire.