[MDPotter]

This is going to be long-winded.

It is not necessary to wire the trinary into both fans, but I prefer it that way. As Ls1nova71 said, it is rare that there will be a situation where the PCM will not be calling for either fan to come on but the AC pressure will be high and trigger the fan(s), but the OCD in me says to hook up both fans to the switch to guarantee that both fans will run on high when the pressure setpoint is reached. That way, you have both fans pulling across the entire radiator/condenser to lower that pressure. In my mind, that will reduce the risk of damaging any AC components.

Here's how my Gen 3 LS works:
-Coolant temp reaches around 190 and the PCM grounds out the low speed control wire (green wire, connector C1 pin 42). This wire remains grounded until coolant temp is below 190. Both fans on half speed.
-Coolant temp reaches around 205 and the PCM grounds out high speed control wire (dark blue wire, connector C2 pin 33). This wire remains grounded until coolant temp is below 205. Both fans full speed.

I found this out while wiring because I was curious. I was able to confirm that both wires have to be grounded in order to have both fans running full speed. If only the high speed control wire is grounded, fan 2 will run full speed and fan 1 will be off. Not a likely scenario, but it's only one more wire to hookup.