Stay with Don's and Agent's lead.....the connection drop will be either corrosion at the batt terminals or fuse link at the solenoid. The solenoid itself will not cause 12v drops through itself but the connections at that same solenoid is where the main power pickup takes place. Stay with the test light attitude and fuse links. If it worked fine before, and now, now nothing, start where you were cleaning. Probably corrosion or hard water build up between contact points at the connection these guys told you about.