I have spent the last three hours trying to find the answer, and have seen 20 different ways it's supposed to be done. I have an 86 Camaro with no computer, I have a tan wire, purple wire, and a blue wire coming from the transmission. The purple wire has been hooked to constant 12 volts by a previous owner, I want to run the lockup with a toggle switch for now.

So how do I wire this so I can lock it up in 4th gear.

 

Run the tan wire to ground through a switch and you can lockup any time you want
You can get the same result by running terminal F on the ALDL through a switch to ground

The purple should run from the TCC switch on the brake pedal as per stock setup so the lockup drops out when you brake; even if the switch is on

 

If I twist the blue and tan wires together would that give me lockup in 4th gear only? The transmission wires are cut off by the firewall so I don't know where they originally went to.