[Accelo]

I used the same 3-relay setup, as Hcb3200, to get two speeds for both fans.
Thanks for posting it.

The OEM Vintage air set up was to run one fan on high or both fans on high.
I wanted to keep the noise to a minimum, so I could hear the "Black Widow -Angry House-wife’s" mufflers. LOL.

How if functions:
When motor is cold and the air is off no fans are running.
Air on "no matter the conditions", both fans on high.
Above 180F both fans run at half speed.
above 190F both fans run on high.
Both these temperatures are ground outputs from the computer. They can be programed differently if needed.

Air-conditioning provisions are supplied by just added the ground from the air Trinary switch to the high-speed relay.
It matters not if the computer is grounding the relay or the Trinary switch grounds the relay. Or even if both are grounded, both fans run on high.
This is important to keep your air-conditioning pressures from going too high.

On can spend $250 on propriety controller boxes or $25 on three relays on Amazon. The down side is the wiring gets out of hand quickly and isn't pretty unless a lot of care is taken. I hid the relays behind the battery between it and the core support. It has worked flawless since day one.

Later year fans are controlled by the ECM/computer and it's a Pulse Width Modulated output that can run the fans at variable speeds.
These require a different setup or dedicated sensors in the radiator.
Cheers