Hi, i fit an led light to the interior light of my fabia but when it dims off it still keeps lightly on, is anything wrong with it? can someone help please?

Nothing wrong at all.

Your normal halogen lights have a fairly high internal electrical resistance. It requires a certain current for them to light up. When the lights are "off" the current going to the bulb is smaller than this required current so you get no light.

With LED's they require a much smaller current in order for them to come on. Its so small that the current which would normally not be enough to light the halogen bulb is enought to light it, all be it dim.

You need to have a resistor wired before the LED's in order for them to go fully off. It's common with cheap ebay led's that they remain on. If you're a dab hand at soldering it shouldn't be a problem, or simply buy new lights if its that big a deal.