Re: 1987 celebrity
1) If you don't have a voltmeter, buy one. (Lowes, Home Depot, or any Hardware Store)
2) Follow the power: 12 volts flows INTO the fuse panel and to one end of each of the fuses.
3) The other end of each fuse feeds the LINE (input) side of the switch.
4) The other terminal on the switch is the LOAD (output) side. It should show 12 volts with the switch ON. If not, the fuse or the switch is bad.
5) From the switch power goes to the device at the end of that circuit (horn, etc.). No power AT the device but present at the switch then the wiring is bad. If power is available at the device, verify the device has a good ground.
For Navigation lights the switch is typically a three position ON-OFF-ON type with either three or six terminals. A three terminal switch will typically have a diode on the back and the wiring is as follows:
Here is Nav light wiring if the switch has six terminals (there are seven and eight terminal switches but let's stick with these two for now).
Here is a typical, single circuit diagram starting at the battery. It doesn't matter what the device (light in this case) is. It can be anything from a light to a motor, or pump, stereo, etc.