There is only one cable on the pump to power it and the 4 fans. The PWM signal is taken from one of the 3 fans of the radiator and these are connected in a chain to a connector that runs along the tubes

Personally I did a push-pull setup, Arctic fans at the back and Corsair high static pressure fans at the front. The Arctic fans are well made, I might as well keep them and use them in push-pull if the case allows it.

I'm not sure why you would want to change them as they are super efficient. (See the test at GAMER NEXUS)
But to answer your question they are connected in series. Each fan has a male and a female plug to allow the series connection. The last one is connected to the pump. I hope this is clear to you.