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Old 03-04-2009, 11:19 AM   #1
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Replacing 7-Pin Connector

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.

Click image for larger version

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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.

Click image for larger version

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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.

Click image for larger version

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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.

Click image for larger version

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Zep
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Old 03-04-2009, 11:23 AM   #2
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Great pictures! Thanks.
I just replaced mine the other day after i went to hit the brakes and the trailer nearly pushed the truck through the intersection. That was enough for me. One of those guys wasnt making a good connection and my guess.. it was the brake wire! lol
Wouldnt have been funny for the guy infront of me though...

Vin
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Old 03-04-2009, 11:28 AM   #3
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Speaking of brakes...

One issue remains. When I put it back together, there was one wire left over. It appears to be a ground wire, perhaps a separate and independent ground for the brakes (it heads into the shell in the same direction as the brake line(s)). Anyone know for sure what this white wire is? My previous photo of the old connector doesn't quite reveal whether or not it was connected to the main ground lug. I assume it was.

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With the tow vehicle attached and running, and a full up 12V system in the Airstream, there was zero volts on that wire.

By the way, this is a 75 Sovereign.

Thanks, Zep
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Old 03-04-2009, 11:55 AM   #4
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Quote:
Originally Posted by Zeppelinium View Post
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.

Attachment 76419

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.

Attachment 76422

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.

Attachment 76420

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.

Attachment 76421 Attachment 76423

Zep
Round pin terminals are superior to the flat pins, hands down, since dirt and sand is an enemy to flat pins, but cannot bother the round pins.

We see flat pin connector failures, everyday.

Andy
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Old 03-04-2009, 11:57 AM   #5
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Where did you get the pretty blue umbilical wire? I need some
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Old 03-04-2009, 12:00 PM   #6
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One issue remains. When I put it back together, there was one wire left over. Thanks, Zep
You are supposed to always have at least one left over.

No seriously, if you think it is the ground going to the brakes you should be able to use a volt/ohm meter to check continuity from there to the ground wire on one of your brakes using a length of jumper wire.
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Old 03-04-2009, 12:21 PM   #7
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Originally Posted by Aerowood View Post
Where did you get the pretty blue umbilical wire? I need some
There's a heavy duty truck store in the Springs that sells it for about $2.68 a foot. Connectors are like $6.

Andy, I'll watch for a connector problem. It's the type I have had on my Ford F250 tow vehicle for 10 years without a problem. What's the alternative if you want to have an umbilical that has a standard tow vehicle end?

Zep
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Old 03-04-2009, 12:27 PM   #8
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thanks

This type of project is the first on my "to do" list before our first trip out this Spring. Thanks for putting the pictures and information out there. Just out of curiosity, do you know why the cord has the connector at the trailer end instead of just hard-wiring the cord into the trailer?

thanks

Laird
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Old 03-04-2009, 12:54 PM   #9
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Quote:
Originally Posted by maccamper View Post
... do you know why the cord has the connector at the trailer end instead of just hard-wiring the cord into the trailer? ...
Umbilicals get damaged, nicked, etc. Connectors get corroded. It's much easier to replace the independent umbilical.

A big issue used to be non-standard connectors. Maybe not such a big deal now, but it's a pain to have to make a short pigtail just to get the wiring to match up.

BTW, VHORD, thanks for the tip. Dope slap for not realizing that the brake (+) is right there at the connector! I can check continuity easily!

Zep
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Old 03-05-2009, 06:16 PM   #10
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A shout out to VHORD here, the white wire was the brake ground. It turns out that the brakes are not grounded anywhere else except right at the umbilical, through this separate wire. At least that's the way it is in my 75 Sovereign.

Zep
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Old 03-30-2009, 10:01 PM   #11
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Oops

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.

Zep
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