Ok, after looking around at possible solutions here is what I came up with.
Thanks Matt for the idea.
Get another fan relay just like the first one.
In this crude drawing I flipped the relay 180 degrees. Just power that new relay from the old relay using the wire that did run the fan.
The ground is the same but the sensor now it the 12 volts of the brake lights just like the old one saw the 12 volts from the compressor. The output of the second relay runs the fan.
Now the fan will only come on IF the compressor is running & the brakes are on.
The fan will come on anytime I hit the brakes if the compressor is running even if it is when approaching a corner. This is not the most elegant solution, but it will keep the fan from running while cruising down the road. It would be cool to figure out how to add a 5 to 10 second delay from the brakes coming on until the fan starts.
OK folks, will this work?