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Tesla stopped supplying 12V power to the aux pin of the 7 way - Fixed!!!

ShawnA

Active Member
Supporting Member
Nov 13, 2017
1,184
989
Edwardsburg, MI
Hello to Model X owners with Model X manufactured on or after March 6, 2018
and no power to the aux pin of the 7 way trailer connector,

I purchased a Model X-100D on February 2, 2018 for delivery March 22 of 2018.
I was fortunate that with a build date of March 6, 2018 I got the new MCU.
Getting ready for the trailer season, I purchased and installed a Prodigy P3 brake controller.

Performing due diligence before trailering, I used a common LED tester to assure all of the proper
voltages and signals were delivered to the 7 pin trailer harness.
I have shown a picture of the tester below.
All pins functioned as designed except the 12V aux pin.
No voltage was being delivered to the 12V aux pin.
I tow a utility trailer that uses the 12V aux power to recharge the breakaway battery and to
power small lights in the trailer.

I had a mobile service visit and we corrected the problem.
Apparently on or around March 6, 2018 there was an engineering change on the wiring regarding the trailer
harness.
As we looked at the short harness to the 7 pin connector, we noticed that the red supply wire from the car
was at the opposite end of the connector to the trailer...
The harness in the bottom picture is "as delivered."
The service technician moved the red wire in the harness to the other end of the connector
where the blue plug is shown and now there is power.
He installed the blue plug into the position where he removed the red wire.

The trailer harness to the 7 pin is Tesla part 1046032-00-C
The harness in my car was dated 11-14-2017.
I do not know if there was supposed to be a new revision of the 7 pin harness that I did not get
but moving the red wire to the other end of the connector fixed my issue.

One helpful detail: The 12V aux pin is supplied by a 15 Amp fuse number F131 in the frunk.
Another detail: There is a Fuse in the Aux box by the right foot of a right hand drive car
fuse F308 Jcase 30 Amp.

Yet another note - The 12V aux power is only supplied when the car is in DRIVE or another selection
where the High Voltage bus is active!!!
So, in an unattended car that is off there will be no power to the 12 V aux pin.

Enjoy,

Shawn
Tester.jpg
Trailer Harness Label.jpg
Trailer Harness-2 .jpg
 
Thanks for this! Just gave up trying to use my electric trailer jack, which uses the +12V to power it and hooked up the F150 for a tow that the X should have been able to handle easily. Came in to search.

I see that the issue is "fixed" but is it really??

Yet another note - The 12V aux power is only supplied when the car is in DRIVE or another selection
where the High Voltage bus is active!!!
So, in an unattended car that is off there will be no power to the 12 V aux pin.

Am I reading this correctly? In order to jack up or down the trailer, I'll need to have someone in the drivers seat with the car in Drive?
Now that sounds pretty safe, NOT... not to mention I often hook up and disconnect when I'm on my own.

Thanks for your research and info, we have a Ranger headed this way in a couple of weeks, I've already emailed them with this issue to add to the couple of delivery tweaks they need to fix up.

Thanks,
JW
 
  • Helpful
Reactions: njxman

ShawnA

Active Member
Supporting Member
Nov 13, 2017
1,184
989
Edwardsburg, MI
Hi JW,

I wish I knew better details of the car...
My Ranger said that the high voltage bus must be ON...
This could be as simple as turning on the air conditioning or heater...
I have not had a chance to figure out much more than it works now with the car ON.
That is what I need to charge the trailer battery while the car is in motion...

Shawn
 
  • Helpful
Reactions: GSP
Thanks for this! Just gave up trying to use my electric trailer jack, which uses the +12V to power it and hooked up the F150 for a tow that the X should have been able to handle easily. Came in to search.

I see that the issue is "fixed" but is it really??



Am I reading this correctly? In order to jack up or down the trailer, I'll need to have someone in the drivers seat with the car in Drive?
Now that sounds pretty safe, NOT... not to mention I often hook up and disconnect when I'm on my own.

Thanks for your research and info, we have a Ranger headed this way in a couple of weeks, I've already emailed them with this issue to add to the couple of delivery tweaks they need to fix up.

Thanks,
JW

Just checked on my MX with a trailer light tester.

Tailgate or door open 12V on
Doors closed and unlocked 12V on
Doors closed and locked 12V on
I did not check with the car sleeping.

All seats were empty for testing.
 

ShawnA

Active Member
Supporting Member
Nov 13, 2017
1,184
989
Edwardsburg, MI
Hi Idoco,

What year is your Model X ?

The harness and wiring change I experienced was a 2018 March 6 build date...

On that date there were new electric diagrams issued and harness changes made that "caused" the failure.

2016, 2017, and 2018 built before March 6 are very different...

There were some claims elsewhere that there were wiring differences on the X P models...

Your voltage may vary, :)

Shawn
 
Hi Idoco,

What year is your Model X ?

The harness and wiring change I experienced was a 2018 March 6 build date...

On that date there were new electric diagrams issued and harness changes made that "caused" the failure.

2016, 2017, and 2018 built before March 6 are very different...

There were some claims elsewhere that there were wiring differences on the X P models...

Your voltage may vary, :)

Shawn
I have an early 2016 MX90D. I realize that (some of) the new MX's have the 12V problem. Presumably due to the wire harness switch documented above. I'm assuming that if the wires are switched back that the behavior will be "back to normal". But that's an assumption.
 
I have an early 2016 MX90D. I realize that (some of) the new MX's have the 12V problem. Presumably due to the wire harness switch documented above. I'm assuming that if the wires are switched back that the behavior will be "back to normal". But that's an assumption.

We ran into this problem with our late-2018 MX. The 7-pin socket couldn't power the trailer or its RF brake controller.

Armed with a multimeter, I traced the "missing" 12V aux from the 7-pin socket back to where the towing wiring harness connects to the vehicle. Indeed, the red wire on the side of the wiring harness plug was on the wrong side, just as described in the first post.

The plug itself is a Molex 034985-1606 connector. I used the drawing to figure out how to pop the front off (the white part, it takes very little force) to gain access to the internal retaining clip for the red wire. Once I got the receptacle terminal for the red wire out, it was just a matter of swapping the red wire and the blue silicone plug and reassembling the connector. I tested with a multimeter again and saw a steady 15.5V on the aux pin, as expected. I reattached the 7-pin socket bracket and everything worked, including the prodigy RF controller.

I didn't have to do any disassembly beyond part of the plug and the two screws holding the 7-pin socket bracket. I needed to move the bracket out of the way so I had enough room under the bumper to fit my hands. The wiring harness itself was attached to the body at its midpoint with a zip-tie, but I didn't end up needing to remove and replace this. There was enough slack in the red wire to swap sides without any further adjustment of the wiring harness.

IIRC, AUX is powered any time the vehicle is "on", even in P.

Good luck! A multimeter is your best friend for this one, but it ended up being a simple repair.
 
We ran into this problem with our late-2018 MX. The 7-pin socket couldn't power the trailer or its RF brake controller.

Armed with a multimeter, I traced the "missing" 12V aux from the 7-pin socket back to where the towing wiring harness connects to the vehicle. Indeed, the red wire on the side of the wiring harness plug was on the wrong side, just as described in the first post.

The plug itself is a Molex 034985-1606 connector. I used the drawing to figure out how to pop the front off (the white part, it takes very little force) to gain access to the internal retaining clip for the red wire. Once I got the receptacle terminal for the red wire out, it was just a matter of swapping the red wire and the blue silicone plug and reassembling the connector. I tested with a multimeter again and saw a steady 15.5V on the aux pin, as expected. I reattached the 7-pin socket bracket and everything worked, including the prodigy RF controller.

I didn't have to do any disassembly beyond part of the plug and the two screws holding the 7-pin socket bracket. I needed to move the bracket out of the way so I had enough room under the bumper to fit my hands. The wiring harness itself was attached to the body at its midpoint with a zip-tie, but I didn't end up needing to remove and replace this. There was enough slack in the red wire to swap sides without any further adjustment of the wiring harness.

IIRC, AUX is powered any time the vehicle is "on", even in P.

Good luck! A multimeter is your best friend for this one, but it ended up being a simple repair.

Thank you so much for this, I've sent the permalink to my Rangers to see if it's something they can do for me. If not, I might pm you for a few more details. I use an electric jack on the trailer and have had to build an adapter to make it work. Would be great to not need that!
Cheers,
NB
 
We ran into this problem with our late-2018 MX. The 7-pin socket couldn't power the trailer or its RF brake controller.

Armed with a multimeter, I traced the "missing" 12V aux from the 7-pin socket back to where the towing wiring harness connects to the vehicle. Indeed, the red wire on the side of the wiring harness plug was on the wrong side, just as described in the first post.

The plug itself is a Molex 034985-1606 connector. I used the drawing to figure out how to pop the front off (the white part, it takes very little force) to gain access to the internal retaining clip for the red wire. Once I got the receptacle terminal for the red wire out, it was just a matter of swapping the red wire and the blue silicone plug and reassembling the connector. I tested with a multimeter again and saw a steady 15.5V on the aux pin, as expected. I reattached the 7-pin socket bracket and everything worked, including the prodigy RF controller.

I didn't have to do any disassembly beyond part of the plug and the two screws holding the 7-pin socket bracket. I needed to move the bracket out of the way so I had enough room under the bumper to fit my hands. The wiring harness itself was attached to the body at its midpoint with a zip-tie, but I didn't end up needing to remove and replace this. There was enough slack in the red wire to swap sides without any further adjustment of the wiring harness.

IIRC, AUX is powered any time the vehicle is "on", even in P.

Good luck! A multimeter is your best friend for this one, but it ended up being a simple repair.

I have the same issue. Is this molex connector located under the car near the 7 way connector?
 
Hi Jlochner,

One of their mobile service people repaired it in my garage with hand tools...
You are able to request a mobile visit to fix it...
Whether that can happen in time for you or not is up to their scheduling...
It never hurts to ask.

Shawn
Same here. Took the ranger maybe 30 mins. It ends up having the +12V fused at the fusebox in the frunk on a 15 Amp fuse that is one of the few you can replace yourself. He showed me which one.
 
  • Informative
Reactions: GSP
And on the subject of when the wire is hot, the car doesn't need to be in drive, but it does need to "On". When you get out it shuts the car down and the screen reads Car is Off where the Drive selection is indicated. Stand outside the car and put your foot on the brake while holding the door open. Seat will adjust to driving position and Drive selection indicator will show up with car in park. The +12V is now hot.
 
Agreed. Would much rather have Tesla take care of this. I reached out yesterday morning via phone to the local service center, as well as via the web portal. Have not heard back from them and do not have high hopes. This is my second Model X and I have never had a good service experience with Tesla. With the flood of Model 3's in my area and only a single service center for all of Long Island my expectations are quite low.
 
Thanks and was it confirmed that the problem did not affect cars before March 2018?
That is what I understand, though I'd certainly test it if is important to you.
I was told that there was a design modification that deleted the hot wire from the pin. A wire appeared to still be there as the tech seemed to only needed to put it into the right place and do some software stuff.
 

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