Here is a basic install using the Supra MKIV kit in the factory antenna hole on a 1993-1998 Supra.
Remove the factory antenna nut; be very careful not to damage the paint with with the pliers. Only turn about 1/8 turn per turn to prevent damage.
Next remove the trunk trim panel screws. Rear, side and wheel well panels are all that need to be pulled.
Be gentle with the screw covers, use a small flat head screw driver so you do not damage the panel.
Don't forget this panel.
Undo the 10mm screws holding the motor assembly then unplug the antenna power harness and the antenna cable connector.
If your antenna mast is stuck in the up position you should be able to pull it the rest of the way out with a simple tug. If not you may need to power the antenna to go in the up position while tugging on the mast. You can now remove the rest of the factory antenna assembly.
Take the lower portion of your antenna kit and place through the antenna hole from the inside of the car.
Place the outer trim and seal in place
Place the retaining nut on the antenna portions, tighten finger tight then check the height of the center; it needs to be close to flush with the retaining nut or you will have a gap under the antenna mast.
Connect the antenna cable
Thread on the mast.......
You are ready to roll