As far as electrical connections, if you have the chance and the energy and time, it is always a good idea to test out the wires to see if there is a 'hidden' internal impedance inside a wire that you don't suspect, like hidden rot or breakage, and after that, I use fine fine sandpaper to brighten up the end bits, then electronic cleaner spray to clean off, followed up by a faint hint of dialectric paste (think of sweaty fingerprints, not a gob of it) before I reassemble. Grounds, grounds, grounds--anything with a star washer gets special attention. It can make for a big difference, along with cleaning dust off old bulbs or simply replacing them, and carefully cleaning dust off indicator light glass and plastic. (Q-tips!). Remember to oil your speedometer as well as the cable (see above) Ask me how I know....
