I just installed a Derale fan switch from Jeg's. I was wondering which wires to the fans are the positive wires. I figured they are the black with the red stripe but I'm not sure. I was also wondering which wire is the positive for the a/c clutch. This is all on a 88 5.7 TPI. The instructions are universal so I just want to make sure I splice into the correct wires for my car.

As you figured out, the black with the red stripe is the positive cable(s). Just put a fan switch in myself. .

Do you have to splice into the fan wiring to use the Derale fan switch or do you bypass the positive wire for each fan and plug the Derale wires directly into the fans and disconnect the factory harness and run a ground to somewhere else?

You may as well leave the wires in place. You will need to run a line from the positive side of the battery to the switch. Then you run the switch flip side to the fans. Splice the line from the switch into both of the positive lines from the fans.Make sure the ground is wired.

If your switch has an LED on it, make sure that is grounded also. This way the lite will work when the fans are on.