Cleaning contacts with a thin strip of a business card is fine when
fixing an isolated problem but when I get a "new" EM that has been
sitting in the barn for five years, I often will run out of business
cards before all the contacts are clean. Worse still is when an unnoticed
bit of paper comes off during the cleaning and opens a switch that worked
fine before you started.
What I do is to take an old toothbrush dip it in a bit of alcohol and
give every contact I can reach with it the once over, after cleaning a
relay I blow everything dry before proceeding on.
WARNING: Be sure to let the alcohol dry completely before powering on the
machine! If the alcohol has not dried you may start a fire!
The first time I tried this I got a machine up and running within an
hour. I wondered if it would ever work again when it arrived.