So, my V6 '91 Daytona has had a consistent problem where the radiator fan will not run unless the AC compressor is engaged. I have dealt with the problem for over 2 years, but just got around so seriously diagnosing it. Thought it might be the coolant temp sensor, but it seemed like it worked fine because the car threw a check engine light when I disconnected it. Replaced the sensor anyways and nothing changed. Checked the fuses, none were blown. Swapped the fan relay and the AC relay with each other, and nothing changed with either system. Checked the relays with a multimeter, and both were functional. Then came checking the wiring. I made sure both relays were getting power from the 40A fuse, and both were good. I then checked the relay to ground continuity though the fan motor, which was fine. To make sure that the fan circuit itself was fine, I stuck a jumper wire in the relay socket and as soon as the battery was reconnected, the fan started. At this point, I knew it was a problem with the activation side of the circuit. Checked the continuity between the SBEC (pin 2) and the coolant temp sensor, which was fine. There was also continuity between the SBEC (pin 31) and the fan relay. So now I have no idea what to do from here. The fan is supposed to engage at 210 degrees under 40 mph and 230 degrees over 40 mph, but it will boil the 50/50 coolant mix and the fan still won't run. I have no idea what else could be causing the issue, so any input would be greatly appreciated.