All tractor-trailer electrical connections need to be secure and properly maintained. Typically, the seven-way electrical assembly is disconnected 99% less on the tractor side than on the trailer side. This means the connection is cleaned only 1% of its life on the tractor, causing it to corrode faster.
The most common warranty claim for a seven-way connector is because of loss of power to the blue circuit, due to corrosion buildup. This buildup starts at the front of the plug connector and is caused by several things: chemical de-icers; a constant current running through the blue pin when the tractor is on; and a major lack of maintenance on the tractor side.
Because all regular plugs and sockets are interchangeable, connections are more prone to size differences—meaning in a best-case scenario you have .3 mm of extra diameter space between the unions, leaving it vulnerable to contaminants. More than 90% of water intrusion occurs around the front of the plug, between the connections.
It’s important that you clean connections regularly using a plug and socket cleaning brush and be sure to apply dielectric grease to dry connections before reconnecting.