My daughter has a 2006 Mustang V6 that has puked it's coolant a few times after running in areas with no airflow (while parked, drive throughs etc.) Found some burnt connectors in the fuse box so I had a local guy wire in an external relay controlled by the computer last fall and it seemed to work as the fan came on, but with the recent hot weather it puked its coolant again due to the fan running too little. It has always been fine when running somewhere with airflow.

I just wired in a fan controller over the weekend set to kick on at 180. It seems to work fine, but it also had another wire that you could run to the AC compressor to have it kick on when it is running. It seems like this wouldn't really be necessary and make the fan run a lot at highway speeds when it wouldn't need to? Also is 180 the right temp to have the fan turn on or should it be a little higher for better efficiency when running? Since I only had one speed to control I hooked it up to the high speed side. Will this cause any issues you can see?

Thanks for the help and opinions!

i don't know exact details of the 06 V6 cars.
i do know there is a resister built into the fan shroud that goes bad pretty often. a red hd wire runs thru the resister before the motor. when this goes bad the fan doesn't work at high speeds.
the melted fuse box is another common problem. with the factory wiring the fan is powered directly thru the fuse box and it melts like yours did. most people wire up a relay to power the fan before it melts. if the main power source for the controller is directly from the battery instead of the fuse box will be fine.

Those cars run much hotter than 180. It sounds like the radiator cap is bad, get one from Ford. You may want to check for combustion gasses in the radiator as well.