Either you dont like how the stock setup requires a high coolant temp or your sensor, sensor sending unit, or wiring from the sensor to ecu/pcm doesn't work but no matter what it is, you want to have control over the coolant fan. Well, here's how to do it on this year camaro. Well, one way anyway.

Couple things about this howto:
it is assumed that under the headlight **** the optional accessory plate is unused.
A 2 position toggle/rocker type switch.

Remove negative terminal on battery.

The fan relay is located under the hood, on the driver side firewall, behind a black flat box. You need to unscrew the box, and using a screw driver, pry up the tab a little holding the relay in place.

You'll want to take out the relay that is closer to the fender, it should have a green with white striped wire, a black with red stripe wire, a red wire, and a brown wire. We'll be splicing the green with white wire as this is the wire that is grounded when the temp sensor tells the ecu/pcm that it's time for the fan to come on. Use a wire splicer if you have one, otherwise you'll need to strip the insulation off and solder the wire we'll be using to connect to the switch.

Once the wire is connected, it's easiest to route the wire around the ridge behind the hood hinge using a glue to tack it in place and down before the door hinge. Bring it back into the door opening under a little ridge in the body metal about level with the plastic molding lining the driver side door. This allows the least chance of causing a leak source.
Glue wire in position there after forcing it under the molding. Pull the plastic molding up to get it under it and into the car, it just snaps back in.

Now if you already didn't, unscrew the plastic dash bottom using the torx driver I know you have for such a situation. There are 4 screws (on mine) which after taken off, the whole bottom just falls.

You should see quite a few ground wires connected to the frame using the standard screw and circular connectors. Find one you like and unscrew it, sandwich your ground wire between the one already there and the screw and rescrew it back in, making sure not to twist the wires around.

Now using a screw driver push the blank accessory plate underneath the headlight **** out by going behind it and pushing towards you.

Take it to a vice or something else to hold it in place and using a really thin screw driver, screw holes around the diameter of the switch you plan on installing, spacing them out only enough so that you can drill another hole without falling into the previous one. Make sure the outer part of the holes you drill match with the diameter of the switch or slightly smaller.

Once you drill the holes, use the drill to grind away the thin walls until the middle piece falls out. This method works well for any shape switch. You can clean up the inside using any number of files or grinding tools on a dremel or what not. Smooth out any ridges on the surface carefully with a flat head or whatever. You should now be able to insert the switch for a nice tug fit.

If the switch has no builtin bezel keeping it from falling through, you'll want to jb-weld or krazy glue it in place. If you drilled too much and the switch is not held tight by friction, glue it.

After the switch is tightly secured it should look really clean and if you got a plastic one with matching color, it'll look really stock.

Now bring the wire you brought under the molding and the wire you grounded up and through the hole where the accesory plate goes. It shouldn't matter which goes to either terminal.

Attaching the wires to the switch may require soldering, do not simply wrap the wire. make sure it's really secured, you dont want to be stuck with a broken sensor or whatever and think your fan is on when it's not because the wires came off.

Test the switch now by reconnecting the negative battery terminal and starting the car. The switch will not operate when the car is off since power isn't supplied to the relay.

If your fan doesn't come on then a couple things could have happened. 1. your fan relay is dead, you should have checked it first by using the AC. 2. your switch is broken. 3. You failed to ground the other wire.

Now that you've tested that your fan is working , simply snap in the accessory plate and tape/tie up the wires. Screw the bottom of the dash back up and you should be left with completely stock looking interior with a new fan switch.

Screw the flat black box back in front of the fan relay

You can clean up the wire under the hood by painting it and hiding any excess. It should be securely glued into position so that the hood doesn't come down on it or the door doesn't get any leaks.

I suspect this howto will work for any V8 TBI in the third gen but I dont know how many models have the removable accessory plate on the dash. If anyone can, confirm other years and if the Z28 can.