my rears are brake and sidelights, should they have two or three terminals? i recieved one with 2 and one with 3, but both plugs for them have 3 terminals...

excuse me if im being really thick, but im terrible at electrics, and this is my first go at it

Should have 3 terminals. One for the brake light, one for the tail light and one that's an earth for the other two terminals.

the 2 pin one is probably a fog light

Rich

cheers...thing is, theres no earth wires at them on the loom...should i add one?

They probably had a tail from the earth to the chassis. That's what most do. Saves running an earth cable all the way to the back. Remember to earth the chassis to the battery earth too.

theres an earth at the back of the transmission tunnel...
there may be an earth from the battery to the engine, connected to the starter motor mount

Just drill the chassis and either stick a rivnut in or a self tapping screw near to each rear light and attach an earth from this to the lights.