I have a Curt Bluetooth brake controller. Works great but last week, it kept going out on me. Figured maybe the unit was bad, being Bluetooth and all. Get unhitched and see that the problem is a cut in the cord on the trailer side of the 7 pin. So I order a new trailer side plug and cut off the old one. Here’s where everything goes to hell.I thought I could pull the end off the old plug to see how the wires are hooked up. But it’s like a solid piece. So I figured the wires going into the end would be in order and proceeded to wire it that way. Plugged it into the tow vehicle, turned on the TV headlights and saw the running lights turn on the trailer. Good. But the other lights (brake & turn) wouldn’t turn on and the brake controller couldn’t make a connection. I disconnected the trailer but the trailer running lights stayed on. Couldn’t figure that one out, so I pulled the bulbs so that the trailer battery wouldn’t die (I’m boondocking).So today, I figure I’ll give it another try. The TV manual had a diagram for the 7 pin (‘02 GMC Yukon XL). Turns out I had it wired wrong. So I rewire the trailer connector to match the TV diagram. But when I plugged it in, the only thing that worked was the left turn/left brake light. At least the running lights were off.So now I’m stuck. Any suggestions?

Keep trying! Took me three days at about 20 minutes a day to get it right. Seems they are all different colors. Now I bring my tester with me.

time to get out the test light and a helper... Ground the test light and then touch each wire from the truck to identify them.the 7 pin should be a 'universal' diagram depending on where the "slot" is on the truck side and then they should match up on the trailer side.should have a diagram on the inside of the cap on the OEM one too?Good luck! Mitch

No helper around. I’m in the Lincoln NF in NM. The Yukon’s cap has a diagram but it’s on the outside and worn down to the point of being unreadable. I’m going to try to take a picture and then mess with it in Lightroom to see if I can get anything out of it. But I would think that would match the vehicles owners manual,so not holding out much hope.

If it were me, I would take a battery and attach the ground wire then connect the other wires to determine what color goes where. I am guessing you will have a marker light, turn lights, break light and you should be able to hear the brakes work.

The wire colours for a standard 7-pin for each pin are on-line (Google), but the joke is in the wire colours GM uses for the pins. Different! You have to wire the trailer 7-pin the standard way, not the GM way.If you ever have to change the GM 7-pin on the back of the truck to a standard one, it gets complicated :) BTDT.Don't get mixed up with the mirror image problem for each side of the connection.

Problems when replacing 7 pin connector | Good Sam Community

17 Replies

wnjj
Explorer II
May 10, 2020
You may have to look for blown fuses on the Yukon if things were wired wrong and plugged in.
CA_Traveler
Explorer III
May 10, 2020
Use a ohm meter and check the wiring in the cut off connector then attach the new one the same way ignoring wire colors on the new connector.
BFL13
Explorer II
May 10, 2020
The wire colours for a standard 7-pin for each pin are on-line (Google), but the joke is in the wire colours GM uses for the pins. Different! You have to wire the trailer 7-pin the standard way, not the GM way.

If you ever have to change the GM 7-pin on the back of the truck to a standard one, it gets complicated :) BTDT.

Don't get mixed up with the mirror image problem for each side of the connection.
lamopar
Explorer
May 10, 2020
If it were me, I would take a battery and attach the ground wire then connect the other wires to determine what color goes where. I am guessing you will have a marker light, turn lights, break light and you should be able to hear the brakes work.
soon2bexpat
Explorer
May 10, 2020
No helper around. I’m in the Lincoln NF in NM. The Yukon’s cap has a diagram but it’s on the outside and worn down to the point of being unreadable. I’m going to try to take a picture and then mess with it in Lightroom to see if I can get anything out of it. But I would think that would match the vehicles owners manual,so not holding out much hope.
MitchF150
Explorer III
May 10, 2020
time to get out the test light and a helper... Ground the test light and then touch each wire from the truck to identify them.

the 7 pin should be a 'universal' diagram depending on where the "slot" is on the truck side and then they should match up on the trailer side.

should have a diagram on the inside of the cap on the OEM one too?

Good luck! Mitch
Lwiddis
Explorer II
May 10, 2020
Keep trying! Took me three days at about 20 minutes a day to get it right. Seems they are all different colors. Now I bring my tester with me.

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Problems when replacing 7 pin connector

17 Replies

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