Rear Running Light fuse Keeps Blowing

Hi All just thought I post this the rear running light keeps blowing a fuse 5amp, the indicators and break light not affected just the running light.
anyone have any idea as to what could be causing this? I fitted a tail tidy and grab rail and rack last year which made the seat a bit of a pig to fit back on. I have just recently put a different seat on which also was a tight fit, am just thinking I my of bared a wire or something on them lines hopefully! electrical faults make me nervous ! any ideas please thanks in advance