'76 Safari Trailer umbilical - no brakes and more

[inthewoods]

Hi folks.. earlier this week I brought home my first airstream. When I picked it up the PO and I couldn't get the brakes to work with my tow vehicle. When I hooked up the umbilical to my TV my reverse lights on the TV came on and stayed on. To me that meant some funky wiring on the airstream side. Also brakes weren't activating. My Tekonsha voyager's light was on indicating something was connected but that's it. no brakes. I found it in me to assume that potentially the Airstream's battery was supplying the 12V to my backup lights so disconnected the battery in the camper and the TV's reverse lights went off.

All the important signal lights were working and I was running out of daylight so called it good enough for my run home. The PO used the trailer a week ago and said brakes were working with his truck...

My TV is a 2000 Chevy Suburban 1500 with factory tow pkg, hitch, wiring, and a Tekonsha Voyager. I also have a P3 controller waiting to be installed. A few weeks ago I was towing a 16ft cargo trailer and had the brake control working fine so I'm pretty sure my setup was working correctly.

This evening I spent some time testing the umbilical on the airstream and found some oddities. From what I understand in the 70's the airstream's wiring doesn't normally match up with today's typical 7way connectors - so no surprise that this one has odd stuff. Opened the service manual for the camper and looked at that for a bit and ended up just checking the umbilical with a tester and small 12V battery.

All the brake, turn and running lights worked correctly and matched up with my TV.

That left the backup lights, Charge line, and Brake line.

I'll try to attach the diagram of what I found to make it easier to describe.

The what is normally the Brake and Charge line on this umbilical are shorted to the ground when checking with my multimeter. All others check out ok.

I was able to confirm the trailer is expecting the charge line on the centre pin of the connector. Radio came on in the camper when I hooked up a small battery!

I was tempted to open up the umbilical and start swapping wires around but with the two unknowns and the shorts I wasn't sure where to go with it. Also finding the shorts got me a little concerned that my TV's wiring was ok after driving a long distance with the shorts in the trailer... but so far TV seems ok.

Also I did disconnect both ends of the umbilical and tested for shorts within the wire itself.. none. the wire checks out though isn't wired straight through.

Any thoughts on where to start?

Thanks for your help!

Matt

[xrvr]

Per chance you blew a fuse in the tv? Never know.

[inthewoods]

Hmm. Good thought. I'll have to check but I did check the TV with a multimeter and all the light pins were ok. The charge line was giving me a constant 12V and the brake control line also giving me constant 12v.

[inthewoods]

Are there usually fuses on the trailer side for all the lights? I couldn't tell for sure when I was reading the 76 service manual.

[ALANSD]

It might pay to open up the access to the umbilical wiring. Ours is a riveted panel on the door side near the front. I found all sorts of crap in there and cleaned it out, then used contact cleaner spray and reconnected everything.
Also spray the contact cleaner in the plug end to clean all those contact points.
I do that before any towing and it keeps everything working well.It solved our issues with the lights.

[TG Twinkie]

The seven pin wiring diagram you posted is old school.
The color codes for today are as follows
White=Common/Ground
Black= Charge Line
Blue= Brakes
Red=Left Turn/Brake light
Brown=Right Turn/Brake light
Green=Tail/Marker lights
Yellow=Aux/Backup lights

While the colors don't really matter it is helpful to be with today's standards

[inthewoods]

I'll have to do that. I pulled the access panel yesterday (it's under the front window for me. But figured I'd have to pull the jack off the front of the trailer to access the back of the connector. At least that is how it looked to me. Here is a picture of the inside access to umbilical.

[inthewoods]

Originally Posted by TG Twinkie

The seven pin wiring diagram you posted is old school.
The color codes for today are as follows
White=Common/Ground
Black= Charge Line
Blue= Brakes
Red=Left Turn/Brake light
Brown=Right Turn/Brake light
Green=Tail/Marker lights
Yellow=Aux/Backup lights

While the colors don't really matter it is helpful to be with today's standards

I should have been a bit clearer. The diagram I posted was just a quick grab from google that I edited the text on. Because i haven't opened the umbilical I don't know what colours are actually used on the connections. I was trying to reference which pins on the 7way were accomplishing a certain function.

[TG Twinkie]

Viewed from the front face of the trailer connector with the key at the top.
The 1 O'clock position= Green
3 O'clock= Red
5 O'clock=White
7 O'clock=Blue
9 O'clock=Brown
11 O'clock= Black
Center=Yellow

[alantbird]

Every AS ive owned (10) I had to re position the wires to match my truck.
trial and error its ONLY 12 volts!

[Action]

Older Airstreams had a different position for wires than the industry practice of today.

>>>>>>>>>>>>>>>>>>Action

[inthewoods]

So after some digging and learning and testing.... I found that the service manual diagram colour coding is accurate for my trailer. Mine has the colours that follow the "US" wiring pattern despite the trailer being a Canadian sold trailer. The wording of the connector on the trailer body though seemed to match the Canadian pin out though. No wonder I was confused. See photo...



The trailer end of the umbilical matched the colour coding of the US wiring.

So in the end at the truck side I had to swap the reverse light and charge + lines to match up with my truck's factory wiring. Not bad... but had me confused for a while till it all made sense.

[inthewoods]

So now that I know confidently which wires are which I can now sort out why the brakes aren't working optimally. More testing to do... but getting closer...

[Wingeezer]

I'm guessing that perhaps your trailer is not wired up according to today's standards!


Might be worth just taking time with some test leads and/or multimeter (and a few beers) to see what's up compared to your Tow vehicle wiring (current standards) , and then, if needed, to rewire the trailer plug accordingly as needed!

Seems like you are on the right track!

Good luck -I'm sure you'll get it sorted out!

[inthewoods]

Success!! I found the brake problem. Super obvious once I got under the trailer and checked all the connections to the brakes. Someone had put a wire nut on and tied all four wires together at one wheel. YES... a dead short in the brake system. Not sure who would ever be silly enough to do that but anyways....

Checked each brake with an ohm meter and got between 3.8 and 4.5 ohms on each wheel. Not sure if that is a good reading but as I understand it some reading is good. Corrected some sloppy corroded connections and redid the wiring at the one wheel that had been all tied together.

Some basic tests at the hitch and brake controller then a 15min drive around town. All seems to check out. Brakes seem as solid as any I've used before on cargo trailers.

So all in all a successful day.... Sorted out the umbilical connection to the TV to restore the charge line, reverse lights, and brakes. Found the short in the brakes and reconnected them all properly. Test drive and she's good to go.

One more thing to check tomorrow - need to see if the original breakaway switch works. I suspect it needs to be replaced but from the wire tracing I did today I know the wiring up to the switch passes current. So swapping the switch if need be will be easy.

Thanks for all the help everyone!