All specs are taken from a Speed Sensity TPI L98.
Coolant Sensor - Located on the intake mainfold on the front. Sends signal to ECM. ECM controls ground to 1st relay to turn 1st fan on/off.
2nd Coolant Fan Switch - Located between #6 and #8 spark plugs. Sends ground signal to 2nd relay to turn 2nd fan on/off. Turns on at 220* and off at 200*.
A/C Pressure Switch - Located on the A/C line between the blower and the evaporator. Controls ground to 2nd relay to turn on 2nd fan. Turns on and off at 216 PSI.
The only way to make the 1st fan come on at a lower temp is to burn a new chip for the ECM. Parts stores carry new fan switchs that come on at a lower temp instead of the 220*/200*. You can wire in a switch to turn the fans on and off manually. To do this, just splice into the ground wire of each relay and run the wire to where you're going to mount the switch. You can use a lighted switch to tell you when the fans are on and off. If you do this, and you run a power souce off of the fuse block, be sure not to run it off of the IGNITION or BATTERY outlets. Put it on the RADIO outlet.