Clean each contact surface with sandpaper etc.
Add a small blob of fresh solder to each contact to slightly raise the profile and plate any remaining corrosion. Use as normal.
Alternatively apply a small dab of copper (conductive) grease to each contact to deter further corrosion and re-apply when/if necessary.
Works for me.If just you want the cheapest way of working out the distances that you are riding, sign up with one of the free online route mapping sites and plot your favourite routes on there!