Please don’t flame me for asking these questions before searching, I have searched for posts but am still confused!

I have a 1987 IROC-Z 5.0 with dual fans. When I start the car and leave it running the fan on the passenger side turns on after a few minutes. I assume therefore that this is primary fan? I am confused because other posts I’ve read state that the fan on the passenger side is the secondary!

The secondary fan I’ve never seen running, hardly surprisingly since the poor weather we have in the UK and the short time I’ve had the car. I tested it today and it works, however I intend to rewire it with a switch on the dash so I can bring it in as and when I wish. Rather then butcher the existing wiring, I want to take the dash switch wires from the fan switch in the block, presumably grounding this will switch the fan on?. However, where is the switch located, do I need to access it from under the car?