My 30 year old umbilicals are cracking and the original Airstream 7-pin connectors are worn and corroded. I’ve been thinking of changing them out for some time. Here’s how I proceeded:
1. Built a new umbilical with identical plugs on each end, that can be used in either direction. It’s really easy to get yourself in trouble by mirroring the wiring–think carefully about which way you’re looking at the receptical vs. the plug. Also, note that three of the current standard colors are reversed in the 70s vintage Airstream connector. Be particularly careful to note that the center pin of the new connector is for backup lights, not the tow vehicle battery line.
2. Cut the shell* of the Airstream-mounted female connector as short as possible, to reduce the protrusion of the connector into the inside of the shell. As you can see in the photo, the shell can’t be cut short enough to allow direct access the lug screws, since there are small keys in the shell that align and retain the phenolic plug.
3. Removed the current female connector. Discovered (duh) that it is mounted in the area of the front steel hold down plate. Turned out not to be a problem–the mild steel is easy to drill through. Also, the existing hole is big enough for the new connector without any modification. Unfortunately, however, the two bolt holes for the old connector are wider than the flange on the new connector. So some kind of exterior cover plate is required.
4. Since I’m a nutplate nut, I added another plate inside with nutplates for the four mounting screws in the new connector. This is not necessary–sheet metal screws through the skin and into the hold down plate would be more than sufficient. As soon as I can get some time with a bucker, I’ll get the 1/8″ rivets installed.
When I put it back together, there was one wire left over. It turned out to be a separate ground wire for the brakes.
* Careful out there, citizens. Turns out it was a bad idea to cut off the end of the connector shell. If you have room for the connector to penetrate a couple of inches inside the inner skin, don’t cut the shell.
Originally, the back end of the shell restrained the wires. Without the restraint of the missing part of the shell, the #10 wire for the tow vehicle charge line is stiff enough to bend the tabs in the connector. Naturally, when replacing the cover and consequently bending the wires (thank you Murphy), the tab touched the shell and blew the 40 amp fuse. Fuses in this physical size are not commonly available any longer.
A wrap of several layers of electrical tape solved the problem.