Does he need to go through any resistance coils if he just wants the motor to have a single speed at the max speed?

If he does not need the resistance coils and wants it to go at max speed he could wire it up like a electric coolant fan but with out the fan controller.

you find a source that is hot when the ignition switch is on and run that to operate the a relay and that is not the high current part of it. Then you wire the fan + with an inline fuse to the relay and from the relay to the fan to ground. The relays can take various amperages so you have to get one that is of a higher amperage the what you need what you need.

In place of the Fan controller/temp sensor you would put an on and off switch.

Of course the blower control on off would be entirely separate from the stock one.

To see some diagrams of that do a goole image search and look for fan relay or electric coolant fan diagrams and so on.

In the diagram terminal 86 would have the on off switch and the current from the Ignition switch source. Terminal 85 goes to ground. And that is the circuit that turns the relay on and off. Depending on what source you use when the ignition is on there may already be a fuse in the circuit.

Terminal 30 has the + high amperage source and could have the fuse in the circuit and terminal 87 is the + high amperage gong to the Blower Motor and the motor itself would have a separate ground.

I don't know a lot about this but I managed to install an electric coolant fan once with a similar relay except that the on off switch is the Fan Controller/Temp Sensor.
When I was looking the relays up they are often referred to as Bosch Relays even though they were not made by Bosch. My van Chevy uses 4 the same relays with variously amperages for different functions so they are common (one of them I remember is the electric fuel pump).

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84 300D, 82 Volvo 244Gl Diesel