blinkers working opposite of tow vehicle

[vanfajo]

I have a 2005 Yukon that tows a '67 globetrotter. Typically when I tow the trailer I switch the lights from "auto" to "on" and that turns on the trailer running lights and everything works as it should. Last night I hooked up and the trailers blinkers work opposite of the truck, the running lights dont come on, and the brake lights dont work. If I switch the truck lighting to "auto" the blinkers work correctly but running lights and brakes still dont work.

Any advice on how to trouble shoot would be greatly appreciated. Thanks in advance for any help!

Best,
Joe

[HowieE]

This test is for a 7 terminal plug system with flat terminals. If your trailer has round terminals you may have to check the wiring positions but the test will determine where the problem is.

With a voltmeter test for voltage on the connector at the bumper of the TV as follows.

While the turn signals are on.
The terminal at 3 o'clock should be the right turn signal.
The terminal at 9 o'clock should be the left turn signal.

If this is correct your trailer connector is wire wrong. If it is not correct your TV connector is wired wrong.

[markdoane]

This happened to me once. I'd put the 7-way plug into the socket upside down.

[vanfajo]

Thanks for the replies.

The plug is keyed so I cant physically plug it in upside down.

I know its wired correctly because its been working properly for the past 5 years...and nothing has changed since last time i used it a month ago?

Perhaps a ground wire issue?

[markdoane]

My plug was keyed also, but it was possible in the dark to put it in upside down. Cheap plastic.


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[jcl]

I would be checking the ground circuit. Also, check the trailer bulbs to make sure they are making good contact. It sounds like the circuit is being grounded through the other bulb contact, explaining the lack of all lights except when the turn signals are on.

[aftermath]

Howie has it right. Go to "the 12 volt side of life" and you will find the schematic for wiring up a 7 plug. Check your vehicle first. It is very likely that your trailer is wired incorrectly.

[aftermath]

Sorry, the 12 volt side of life did not have the schematic for your connection.

This one will

https://www.etrailer.com/faq-wiring.aspx

[dannydimitt]

my 2 cents go with the bad ground being the culprit , simple test , simply ground your trailer to your vehicle with a jumper cable "frame to frame" and see if this erases the problem . if it does, check where your ground wires actually connect to trailer and tow vehicle .

[mrfixit51]

Most likely a ground problem. With a bad ground other lights will illuminate that are not supposed to. Happened a lot on older vehicles, with bumper attached signal lights.