Nice car. I likes Mitsubishi's. Lots and lots :-)
Here's how I would do it.
1. Pop the bonnet of the car. Look at the back of the headlight assembly, and note the colours of the wires that go to the headlight bulb.
2. Pull the headlight bulb out of the lamp assembly and pull the lamp out of the lamp holder.
3. a.) If you want to have the foglights on when your dip beams are on, turn your headlights on to dip/low, and test to find which wire on the lamp holder has +12 volts on it. To confirm that this is the dip/low beam wire, turn your headlights onto park. If there is now no voltage on the wire that previously had +12 volts on it, that wire is your dip/low beam supply. If there is still +12 volts on the wire, then that wire is your park light supply. Repeat until the dip/low beam wire is identified, and then note down which colour/combination of colours that wire has.
b.) If you want your foglights to come on when your high/full beam is on, follow 3a, but with the headlight switch set on high/full beam as opposed to dip.
c.) If you want your foglights to come on whenever your park lights are on (ie whenever you have your car lights on), follow 3a, but with the headlight switch set on park to start with, and to confirm that the correct wire has been identified, turn the headlights off completely.
4. Next to where you want your relay to be mounted, carefully unwrap the wiring loom to expose the separate wires.
5. The wire that matches the colour/s of the wire identified in 3a (or 3b or 3c!) is the wire that you want to tap into for the relay's coil supply.
Using a Scotchlok connector, tap into this wire to obtain a +12 volt signal for your relay.
If you can't find the wire in that group of wires, tape them back up with insulation tape, and try another place closer to the headlights and repeat 4.
6. Run the other necessary wires for the relay alongside the original wiring loom until they reach the required destination, and tie securely every 4-6 inches.
7. Mount and connect the relay according to the manufacturers instructions. Including a fuse between the battery and relay.
I'm not too sure of the connections etc on the relay itself, it should have a diagram with it somewhere, either on the packet or in it.
A scotchlok connector is a crimp connecter that cuts through the insulation on a wire, which means that you do not have to do any cutting of wires to tape into them.
P.S. this is how I would do it (as an industrial electrician), if you need any more help, let us know.
Happy huntin