Good grounds are essential but so is good contact at the fuse box. Short of buying a refurbished one from Ron Kwas, which is probably a permanent fix, I removed the fuse boxes from both of my cars, then soaked them in a mild concentrate of phosphoric acid. I used a product sold by Sherwin Williams at their auto paint store meant to etch and clean metal before painting. This, hopefully, cleared out the corrosion in the concealed spaces. Then I used a wire brush on a wheel to finish brightening the fuse box terminals. I also did the female spade ends, I had to hold them in the acid for a while then brushed them by hand. I did the fuses too. In all cases, before the wire brush treatment, I thoroughly rinshed the acid off with clear water then dried with a hair dryer. I reassembled with Burdy Penatrox as described by Ron on his site. Things that didn't work are now magically working, although I still have a few issues to deal with.