Adding a toggle switch to control the radiator fan

[insyncro]

I have searched, found nothing and while transferring my files from one computer to another have lost some old data, this wiring upgrade schematic unfortunately...

Can someone post a link, diagram or just explain the proper way to connect a toggle switch to turn on the rad fan.
I am going to do this in a carat van and do not want to just turn on the AC.

I still want the thermo switch to be inline and the AC to activate it as well.

Ideally I would love to have different speeds with the toggle and I have multi position toggles, but just on off works for now.

Thanks in advance.