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Discussion Starter · #1 ·
I have a 2009 Frontier that I bought new. I installed the factory wiring kit and electric brakes. About a month ago the trailer turn lights and brake lights stopped working. All lights on the truck are working The running lights and electric brakes still work. I could not figure out what was going on so I replaced the factory trailer wiring and the jumpers to rule those out. That did not correct the problem. There is no power on the signal or brake at the rear of the truck. Any suggestions before I start looking at wiring harness on the truck? Thanks
 

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I'd check in this order. Fuses, multimeter at the connector and see if you have signal. THEN you can turn to the bcm, if theres no signal at connector OR look at trailer wiring if connector signals are good.
 

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Rare for the BCM to die, unless you did the crap install and taped directly into the tail lights. Factory wiring is engineered to protect the vehicle from bad trailer wiring.

There are multiple layers of fuses and even fusable links. Behind the glovebox is one batch of fuses. Another under the hood. And a few fusable links as well. Test light is your friend. Don't even read the label on the fuse. Just touch the test light to both pins on the back on the fuse. Look at the fuse, the conections go all the way through. Test the fuses while they are in place. When you find a fuse that has power on one side but no the other, that one is bad.

The fusible links do require pulling.

Still didn't find it and someone still telling you it is the computer? Find the turn relays. Take one out. Two terminals are for the contacts, one should have power and the other goes to the trailer plug. The other two are for the control coil. One of those has power, the other is grounded by the BCM. Be careful playing around in there, try jumping the wrong pins and you could fry the BCM. The signal from the BCM to the relays is different than the turn signals on the truck. Part of the same logic, but has to work with the brake lights as well. So a different circuit just sharing some of the logic.
 

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Discussion Starter · #7 ·
No bad wiring on my part. Used the Nissan tow wiring harness. I replaced the truck wiring at the rear, from to frame to the 7 pin trailer connector and also the jumper wires up in the passenger panel. This is the trailer tow package. So $70.00 to replace the wiring to rule that out. I have pulled some fuses but did not find anything but will try a test light on them. I will also check to see if a mouse or something got into the wiring. Anyone know which relay is the turn relay? Thanks
 

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2012 Nissan Frontier
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Let me know what you find. I have the same issue, but have not prioritized digging into it yet.
 

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Discussion Starter · #9 ·
I fixed the issue today. V8Man and the others were correct about it being a fuse. It was not a fuse on the inside fuse panel and also it was not the fuse box on the firewall. That one base a bunch of fuses and relays. Right on front of that box is a small fuse box. This one only has one relay (room for 4) and one fuse (Room for 4). It was an 15 amp fuse for the BCM. Hope this helps
 

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2012 Nissan Frontier
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I fixed the issue today. V8Man and the others were correct about it being a fuse. It was not a fuse on the inside fuse panel and also it was not the fuse box on the firewall. That one base a bunch of fuses and relays. Right on front of that box is a small fuse box. This one only has one relay (room for 4) and one fuse (Room for 4). It was an 15 amp fuse for the BCM. Hope this helps
I'm confused on which fuse location you're talking about. Could you snap a picture?
 

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Discussion Starter · #11 ·
Sorry I have been out of town. Attached is a diagram of where this fuse is.
It is called a relay box and its infront of the fuse box in the engine compartment.
Text Line Diagram Font Parallel
 

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2018 Frontier 2wd king cab
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Rare for the BCM to die, unless you did the crap install and taped directly into the tail lights. Factory wiring is engineered to protect the vehicle from bad trailer wiring.

There are multiple layers of fuses and even fusable links. Behind the glovebox is one batch of fuses. Another under the hood. And a few fusable links as well. Test light is your friend. Don't even read the label on the fuse. Just touch the test light to both pins on the back on the fuse. Look at the fuse, the conections go all the way through. Test the fuses while they are in place. When you find a fuse that has power on one side but no the other, that one is bad.

The fusible links do require pulling.

Still didn't find it and someone still telling you it is the computer? Find the turn relays. Take one out. Two terminals are for the contacts, one should have power and the other goes to the trailer plug. The other two are for the control coil. One of those has power, the other is grounded by the BCM. Be careful playing around in there, try jumping the wrong pins and you could fry the BCM. The signal from the BCM to the relays is different than the turn signals on the truck. Part of the same logic, but has to work with the brake lights as well. So a different circuit just sharing some of the logic.
I used the factory 999t8-br004 harness and our frontier did the same thing. No brake/ turn signals. Still haven't figured out why.
 

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2018 Frontier 2wd king cab
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HAve you started with the fuses under the hood mentioned above? Pretty common to have bad trailer wiring cause a short that blows the fuses.
All fuses and relay's are good that's why it's puzzling as to why they won't work. I went through and completely reworked all the trailer wiring today. I tested the pigtail at the hitch and it has no power at all on the truck side. I can put 12v to the trailer lights and they work.
 

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2018 Frontier 2wd king cab
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Ok. I installed the new 999t8-br004 tow package harness. I now have working running lights but still no turn or brake lights. I literally pulled and checked every single fuse in all 3 fuse boxes and none where shot. So what else could it be?
 
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