Most people don’t think about the fat black cable that connects the Airstream to the tow vehicle—until something doesn’t work, like taillights or brakes.

It’s called either the “umbilical” or “7-way” cable, and keeping it in good condition is important because it’s the critical link for correct operation of trailer brakes, lights, and signals.

The 7-way, explained—

Since 1989 all Airstreams have used the same wiring arrangement. (Earlier trailers may have different wiring, but typically they have long since been rewired to fit modern tow vehicles.) Each location in the 7-way plug is dedicated to a specific signal. Two of them—the 12 volt positive and 12 volt negative—supply power to keep the battery charged while towing to prevent depleting the battery while using the electric brakes. The other pins carry signals to activate the clearance lights, turn signals, brake lights, and back-up lights (if the trailer is equipped with them).

Is your cable too long?

Take a look at the 7-way cable the next time your Airstream is hitched up. Does it drag on or very near the ground? It will wear away quickly if it touches the ground during ordinary towing. You can use a bungee cord to take up the slack. (Drooping to touch the ground only in a sharp turn is okay, since that contact with the ground will be very brief.)

The cable should have enough slack so that the tow vehicle can make very sharp right and left turns in a parking lot without pulling the cable taut. If your cable is too short, you can buy an extension cable or (better) have the entire cable replaced. On vintage Airstreams, old stiff cables are common, so replacement is a good idea anyway.

When hitching up…

…double-check that the plug is inserted fully each time. Often it feels like it is in all the way when it really isn’t. To be sure, kneel down and look at the connection from the side. There are little tabs on the plug and the lid of the receptacle on the tow vehicle, which lock the plug into place. If the plug isn’t inserted fully, you’ll be able to see it from the side much more easily than from the rear, and this will ensure it doesn’t come loose while towing and make sparks on the freeway.

Avoid corrosion

Corrosion is the major cause of problems for the 7-way plug. Just a little moisture over time will result in greenish or white corrosion on the connectors, and that will cause problems like inoperable lights or brakes.

Be sure to position the plug between trips so that the head of plug is hanging downward. That will help keep rainwater from settling in the plug. At various RV stores you can find a generic “7-way plug holder” that mounts to the A-frame, which gives you a place to lock the plug when it’s not in use.

Periodic maintenance…

…for the 7-way plug on the trailer is important. Periodically you should clean corrosion from the seven spade connectors. It’s difficult to do without the right tool, so we recommend a kit available in the Airstream Life Store which includes a burnishing tool (a special file designed for electronic use), a premium electrical contact cleaner, and instructions.

You can also use the same tools to clean the connectors in the tow vehicle’s 7-way outlet, if they need a little help. Plan to do this simple cleaning job at least once a year as preventative maintenance. With the right tools it takes just a few minutes.

With those simple checks and a bit of annual maintenance, you’ll have eliminated the most common causes of problems with trailer lights and brakes.