What do y'all use to clean the metal connectors that go into the bulkhead on either side of the fw?

Cleaning bulkhead connectors

Also this may be helpful
question on the main harness plug on firewall

I've also been using Deoxit products more recently. Some of them leave a residual protective coating on the metal. This was after discovering dielectric grease is not actually always a good protection against moisture. Its good for spark plug boots and high voltage situations, but not a moisture seal.