1998 Chevy Venture Cooling fans not working

I just recently purchased a used 1998 Chevy Venture Van. The previous owner has hot-wired a switch to the cooling fans so they run constantly once the vehicle is running. Can you tell me what could be the problem thats keeping the fans from blowing.
I would like to remove the wiring and get the van back to the regular way of cooling without using an external switch. Thanks