1G radiator fan won't turn on

[1slowdsm]

Where was this bad ground it turned out to be? My fan isnt coming on right now. Checked everything, replaced thermostat, even replaced the harness (part that plugs into fan). Fan wont even come on when I use jumper wires at the fuse to start up the fan or when I turn on the A/C fan.
How do you connect the fan to a switch to manually turn it on? I'll need to bypass the stock harness if it's part of the connection to the switch.