The nearside headlight on my Bongo is a bit dim (along with its owner

It's noticeably dimmer than the offside one both on dipped beam and full beam (doesn't appear to get any brighter at all, although the offside is fine).
After a bit of searching online I think it might be an issue with the ground connection? Has anyone else had this problem? And where should I look for the right wire/connection to poke/scrub???
Thanks in advance!!