You blew the relay.
The proper way to run e fans is to wire in a relay to each fan.
In some cases, a 30amp relay is just barely enough for the current draw.
I installed a radiator fan switch in the water elbow, and ran two independent relays off there, each with it's own direct line to the battery.
Problem with that location for the rad switch is that the fans would run for at least five minutes after shutdown, because the fans can't cool the reference(water elbow) coolant.
The proper way to do it is to weld a bung into the radiator itself, and wire the radiator switch at that location. That's why car companies do it that way.
But then I got smart and put a new oem shroud and belt-driven fan on. never had a problem since,