FYI: The previously-provided link to the ground points changed; I just now updated it in my previous post: http://www.cabby-info.com/electrical.htm#Ground .
FWIW, here is what the factory battery-to-frame-to-trans cable looks like:
(disregard the cut section; I cut the cable rather than removing the air box/fuel distributor to get the cable out)
If your ground cable(s) look like this:
...replace it/them! Consider putting the new cables inside wire looms to protect them from grease and other contaminants.
I just got through replacing the main grounds on my Vanagon (they were disgusting), and cleaning up all other ground connections, as well as the alternator connections (van spent its life along the CA coast; every metal thing in it has a bit of corrosion on it). Took it for a drive yesterday and noticed that the dash lights are brighter! Moral of this story: Head to your local paint department, grab a wire brush or two and get to cleaning your electrical connections! (Disconnect battery first!)