When you say wire brushed down, do you mean you have taken the bolt out, wire brushed the earth cable surface that touches the chassis and wire brushed the chassis where the cable will bolt to? Wire brushing the top of the earth point will not achieve a great deal.And as you say it - the lights are a little bit dim for my liking, id say 70% of how bright they were originally - Im hoping this is a clue?
If its an earthing issue, is their an area I need to start at and work back from - IE a main / most likely culprit?
For earths, any I've come to so far have been wire brushed down, but as of yet I've not found any that are badly corroded.