I have noticed a few posts regarding the use, or misuse of dielectric grease. The term "dielectric" refers to to opposite of "electrically conductive", in which it is actually an insulator!! A common specification used in the electronics industry called "dielectric breakdown" refers to how much voltage per mil thickness a material can insulate before voltage will "leak" through. The common dielectric greases found at auto parts stores are usually a silicone grease. It is called dielectric grease because it can be used AROUND electrical contacts without concerns of voltage carrying through the grease and finding a short. Consider it like a liquid insulator!
There are some greases that are designed specifically for multipin connectors and switches with a LOW dielectric breakdown. These greases are formulated to purposely conduct at very low mil thickness (close proximity of a socket/pin connection), but otherwise have high enough dielectric so as not to create shorts through the entire connector. Grease is used to lock out moisture.
The reason I bring this up is I notice several people advocating the use of dielectric grease for "all connections", without consideration of what grease is used. In short, the common variety of silicone grease actually has a HIGH dielectric breakdown as it is intended for spark plug boots so if you put that on a metallic connector, you will actually create RESISTANCE, which is opposite of what you want! This can cause all sorts of electrical problems.
Now, I realize some tech sheets for spark plug wires may even promote the use of this grease, but their goal and intention is to rely on a high pressure contact to squeeze the grease away from the actual point of contact. And also realize spark plug wires operate at many thousands of volts. Apply that same method to a connector with only 10-15V, and you have effectively installed a resistor in the connector.
There are greases formulated as "electrically conductive", and are commonly used in electronics. They are not as common in automotive applications because any accidental overage can create an easy short.
The proper use of common silicone dielectric grease would be to apply the grease ONLY on the connector boots to create a high quality water seal, but it should not be applied to the actual metallic contacts.
Brandon
Mull Engineering