'71 Tow vehicle/trailer 7 way connector wiring

[Lumatic]

Worked on my 7 way connector today and found some odd things. It looked to me like a PO was fiddling with it.
1. There were 2 red wires for a turn signal. should only be one I guess. Only one for the other turn signal. Disconnected one and it didn't seem to make any difference. Why? Did the factory or AS put in 2 lighter guage wires to make it the equivalent of a heavier wire, or could the other wire do something else?

2. When I went inside and took off the 7 way access cover I found the white ground wire I fiddled with for 15 minutes on the outside was not connected to anything. There was another heavy guage white wire from the wiring harness which is too short to reach the exterior 7 way plug. Could the loose wire be someones idea of a ground extension piece to connect the too short wire? Right now no ground wire is connected and the exterior lights seem to work fine. I am guessing because the system has redundant grounds and the TV ground and trailer ground are connected by the tow hitch contact anyway. I think connecting the white ground wires to the 7 way shouldn't hurt anything? (famous last words) I'm not sure but I suspect the PO had a problem blowing the small 40 amp fuses in the Univolt, but not sure why.

Anybody ever encounter a situation like this? I wonder if this was the factory or a PO's work around of a problem I am not aware of.

3. There is some kind of electronic device in the trailer wall near the 7 way. from the wiring schematic I figure it to be a 25 amp circuit breaker. Kind of a strange, inaccessable place to put one. Anything else it could be? Like secret alien spyware. I am not too far from one of the three purported Roswell alien crash sites you know.

[nickcrowhurst]

Originally Posted by Marshall

There is some kind of electronic device in the trailer wall near the 7 way. from the wiring schematic I figure it to be a 25 amp circuit breaker.

Marshall, that is probably an auto-resetting thermal circuit breaker. If there's excess current it gets hot and opens the circuit. Once the device cools down, it automatically re-makes the circuit. It's a little black rectangular gadget, about 4 cm by 2 cm, IIRC, and on my trailer it's screwd to the wall near the charger.
Nick.

[gretchen]

Marshall, the little red wire needs to go on top of the big white wire.Thats how it did on my 72 Overlander , the small red wire is a ground for the brakes.If igured this out the hard way. Hope this helps.

Dewayne

[BMW Sid]

I just looked in the wall cover today for the first time on my '73 TW. The circuit breaker is permanently open, fried because I paid a guy who is supposed to know how to do this stuff, connect the brake control, etc. He has the main center post as a ground, and it is supposed to be 12V to the battery. No wonder the univolt died! ( Replaced with a charge wizard) No wonder I have been having trouble with getting a charge to the battery! I might get it all sorted out this year!

[Ganglin]

7 Way Systems

Round 2" diameter connector allows additional pin for auxiliary 12v power or backup lights.

7 way RV flat blade tow vehicle side.
7 way RV flat blade trailer side.

[87MH]

Unfortunately, Airstream had their own convention.

Double click on the below images to enlarge.

Whenever you get a "new" old trailer it's always best to check out the functions with a cheap voltmeter and/or a fused circuit probe and battery.

Also included is a pic of the trailer fuse block showing the internal color codes and fusing of the trailer/towvehicle connection once the 7 way enters the trailer.

Other years may vary.

[Distantdrummer]

Marshall (Lumatic) which of your two trailers are you speaking of in this thread?
~edit~
I see now you mean the '71.

I am searching for that thermal circuit breaker on a 75, not found yet.
I wonder if they are always near the 7-way male (trailer side) access box?

BTW
Anyone know if electronic Contact Cleaner (aeresol) is harmful to the plastic sockets that the 7 ways are usually made of?

[mello mike]

Originally Posted by Distantdrummer

I am searching for that thermal circuit breaker on a 75, not found yet. I wonder if they are always near the 7-way male (trailer side) access box?

Yes, they are normally found attached to the front access cover for the 7-pin connector. My '72 didn't come with any thermal circuit breakers (don't know if they were removed by a PO or not). I ended up installing one for the 12v tow line.

[Distantdrummer]

OK it looks to me that a circuit breaker in the 12volt-Tow-Line (pigtail, lifeline) unit could result in a bad situation. Got to figure the time it would overheat & open would be during towing on the road. So operator would be without stop lights, brakes, turn signals and every other trailer item.
Assuming the pigtails were constructed correctly with the right gauges of wires (three 14s, two 12s and two 10s)(if I remember Inland Andy's recipe correctly) then what would cause the circuit to over heat and throw (open).
I am also assuming that the operator does a walk-a-round before each tow and checks all lights. Not sure how one would check the brakes in a walk-a-round.

[Splitrock]

On my trailer there are 7 wires that come from the tow vehicle. One is a ground that goes right to the trailer 12 volt system as a ground and is tied to the body (as a ground). One is the right brake/signal light and is fused. One is the left turn/brake light and is fused. One is the tail/running lights and is fused. One is the back up lights, and is fused. One is the brakes and is not fused. One is the 12 volt line tied to the tow vehicle voltage regulator, used to charge the trailer battery, and is fused.

None depends on the other. If the 12 volt charging fuse blows, the battery just won't charge, but the brakes and all the trailer lights will work if they are properly wired and connected.

[Splitrock]

To check my brakes, I just slide my brake controller while the tow vehicle is connected to the trailer and the rig is moving.

[Distantdrummer]

Splitrock it sounds like the thermal circuit breaker mentioned above is before any fuse panel and if I understand correctly it would knock out all the 12-volt in the trailer. If that is the case I don't understand it's relevance.

[Splitrock]

Originally Posted by Distantdrummer

Splitrock it sounds like the thermal circuit breaker mentioned above is before any fuse panel and if I understand correctly it would knock out all the 12-volt in the trailer. If that is the case I don't understand it's relevance.

My trailer has a fuse on the battery positive connection right above the battery box, which is below the kitchen range, curbside.

If I loose that fuse I'd lose interior 12 volt unless I'm on shore power. If I lose 12 volt in the trailer, my exterior lights and trailer brakes will all work if the trailer is attached to the tow vehicle. If I lose my battery, the break away switch won't work in a towing break away.

My trailer has two separate 12 volt electrical systems.

Gary