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I have all three relays in my 2012, AT, since 2017, no problems. pull 3 different trailers, OEM harness' tho. I wish you luck,
 

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2018 Frontier 2wd king cab
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Discussion Starter · #82 ·
Guess we’ll see what happens when you hook it back up sans that 3rd relay. That would be a super strange fix that makes no logical sense to me, but if it works…..
Doesn't make sense to me either the issue with it doesn't make sense either. I was sure it would be the bcm. I ruled that out when I pulled the kit and the brake/ turn signals started working normal again. I think something in that kit might be ???
 

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Discussion Starter · #83 ·
Also wish someone on the site would move that damn banner at the bottom of the screen. I'm on mobile and everytime I go to hit post it pops up right in the way.
 

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Discussion Starter · #86 ·
Oddly acting lights can often be due to a ground problem, but your other functions are normal, so that's prolly not indicated...
That's what I'm reading lately is to not ground the lights or trailer plug to the trailer. Ground to the pigtail harness only.
 

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Discussion Starter · #87 ·
Don’t know if you ever got your issue solved but after stumbling upon, and reading this whole thread, only logical issue with the lit up turn signal is the BCM sending power to the left turn/brake relay when it shouldn’t be. I would expect bad BCM. Was this ever solved?

For anyone wanting more info than etrailer’s cluelessness, the 3 relays in the towing kit are for trailer running lamps, trailer reverse, and trailer Aux 12V. When they say to only plug in two of the relays for automatics and use all 3 for manuals, you can plug in all 3 on autos just fine.

The automatic outputs it’s reverse 12V via the TCM which goes to the trailer reverse wire too. The manual has a simple continuity pushbutton switch on the side of the trans like every manual ever, and they don’t want much load flowing through that so they use that to trigger a relay which is in the tow harness kit to provide the trailer backup light power. So on an auto if you plug in that 3rd relay it will just do nothing as the autos are wired to not touch that. The manuals need it or else you won’t get full functionality.

The other two relays are needed on both transmissions for full functionality. If you skip either of them, you won’t get running lights or you won’t get aux 12V depending on which relay you skip.
Never seen a trailer with backup lights.
 

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Discussion Starter · #88 ·
Don’t know if you ever got your issue solved but after stumbling upon, and reading this whole thread, only logical issue with the lit up turn signal is the BCM sending power to the left turn/brake relay when it shouldn’t be. I would expect bad BCM. Was this ever solved?

For anyone wanting more info than etrailer’s cluelessness, the 3 relays in the towing kit are for trailer running lamps, trailer reverse, and trailer Aux 12V. When they say to only plug in two of the relays for automatics and use all 3 for manuals, you can plug in all 3 on autos just fine.

The automatic outputs it’s reverse 12V via the TCM which goes to the trailer reverse wire too. The manual has a simple continuity pushbutton switch on the side of the trans like every manual ever, and they don’t want much load flowing through that so they use that to trigger a relay which is in the tow harness kit to provide the trailer backup light power. So on an auto if you plug in that 3rd relay it will just do nothing as the autos are wired to not touch that. The manuals need it or else you won’t get full functionality.

The other two relays are needed on both transmissions for full functionality. If you skip either of them, you won’t get running lights or you won’t get aux 12V depending on which relay you skip.
The post #66 is the information that came with with the 999t8-br004 Nissan harness.
 

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Never seen a trailer with backup lights.
They don’t have backup lights, 5-wire trailers use the backup circuit on boats. I forget what it is but there’s something on some boat trailers that will lockup in reverse, except when the backup wire has power. It’s something along those lines, too busy to look it up and be more correct though.
 

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Discussion Starter · #90 ·
They don’t have backup lights, 5-wire trailers use the backup circuit on boats. I forget what it is but there’s something on some boat trailers that will lockup in reverse, except when the backup wire has power. It’s something along those lines, too busy to look it up and be more correct though.
Ok I gotcha it serves as a different function.
 

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Discussion Starter · #91 ·
Ours is a 4 pin I keep thinking it's going to end up being the bcm. It's at the shop now so maybe they will figure it out. If it is the bcm I can't figure out why Nissan didn't think of extra fuse protection for the bcm on the tow package side. Or bcm in general I read somewhere they are doing bcm fuse updates on the Titan trucks.
 

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Discussion Starter · #96 ·
Correct, but at one point you said something along the lines of “why does it start working when I pull the relay then?”
Actually I pulled the complete harness behind the kick panel out. The brake and turn signal function went back to normal without park lights. But when I hooked the trailer up this spring is when the brake and turn lights didn't work at all.
 

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Discussion Starter · #97 ·
I still believe it's the bcm I scheduled a diagnostic with a different dealer on the 23rd. For some reason the dealer it's at now said they didn't have the software for the diagnostic check for the 2018. Didn't make sense but I will pick it up tomorrow and take it to the other dealership the 23rd. Maybe it will get fixed.
 
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