Basically my passenger side sidelight is dimmer than the drivers side?

The car has an extra pair of sidelights wired in (spliced into the current sidelight looms) and using low volt LED bulbs, and for a few weeks they were fine, then i noticed 3 out of 4 were bright as usual but the passenger side headlight one was dimmer than the rest, tried a few bulbs and swapping bulbs around so its not the bulb?after a week or so the bulb packs up. Its on a Focus.