installing towbar on Navara

Sorry just reread your post, I cant help with which particular wires on a navara to splice into.
However if you look at the wires going to your tail lights, stop lights, L + R indicators, reverse lights etc take note of the colour codeing and follow them back from the bulbs to the main loom and splice in there.
Good luck

Once you have followed guzzi's instructions and wired up your plug (make sure you wire an earth to the plug because relying on your tow ball for an earth gives you all sorts of problems) this little trick will confirm which plug pin is connected to which light on your car (it is also good for testing your globes on the rear of your car but not the supply to those globes)

grab a length of wire (10 or 15 amp) long enough to reach from your cigarette lighter around your car to your tow bar plug. On the cigarette lighter end connect a 10 amp inline fuse at the other end of the inline fuse connect a suitable plug for connecting to the cigarette lighter socket (you may have to have your ignition on to power the lighter socket)

At the other end of the wire connect to one terminal of a heavy globe say one filament of a 55 watt head light globe on the other terminal of the globe connect another piece of wire about a metre long and bare about 10 millimetres at the other end of of your 1 metre wire.

So what you have when you connect the plug to the cigarette lighter socket power flows out through the fuse (so if you jam the wire in the door hopefully the 10 amp fuse will blow and not your cigarette lighter fuse) through the 55 watt light to your bared end (the purpose of the 55 watt globe is to limit current so that you can touch anything on the back of the car without causing a short but heavy enough to supply power to work the globes on the back of the car)

First thing touch the 10 millimetre bared end on a clean part of your tow bar and the 55watt globe should work and you know you have power (if not turn on your ignition or make sure the plug is fully home in the cigarette lighter socket)

Make sure your headlights and trafficators etc. are off ( no harm will come if they are on except for a false indication)

Next sequentially touch the wire on each of the (clean) terminals of your tow bar socket.

When you touch the earth terminal the 55w globe will glow bright (as bright as when you touched the tow bar) as you touch the other terminals you will see the lights light up that are connected to those terminals you can make a diagram and check them against the diagram for a 7 pin socket

You can also use this for testing the pins and lights on your trailer but its very important to make sure you connect a good temporary earth to the trailer because the tow joint can be misleading