De-Oxit is a cleaner for electrical contacts/connections. Di-electric grease is a grease for electrical connections to "seal" them from moisture, etc. Despite what some folks think, It is NOT conductive and is not supposed to be. It should be used on virtually any electrical connection that is or can be exposed to the elements. If you pull the electrical connectors on any recent automobile, you will find the connectors stuffed with di-electric grease.
It is NOT smeared on AFTER making a connection. It is placed on the connectors (whatever type they are - push type, screw terminals, yes - Lucas bullets, etc) and the connection is then made normally. The mechanical connection displaces the grease at the point of contact and the Di E grease then seals the connection. There must be a good mechanical connection in the first place.
A typical process when working on car/boat/bike electrical connections is: Break the connection, do any serious cleaning or replacing of connectors that may be needed (wire brush corrosion, or cut wire back/install new terminal for example), spray connectors with De-Oxit, wipe off if they are screw terminals if push terminals make/break connection several times, break connection and coat connectors with Di E grease, remake connections.