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Discussion Starter · #1 ·
Truck: '07 Crew Cab XE - standard transmission, 4 pin lighting system.

Issue: new trailer (to this truck), brake and turn signals are fine but no running lights. Trailer lighting installation is just fine, works like a champ on other vehicles and from a stand alone battery.


Research: This forum and others seem to point problem areas, a) fuses/fusible links, b) installed relay systems vary widely, c) the usual broken wires, loose or corroded connections etc.

Forums and discussions seem to indicate that while there are number of commonalities, there are a number of different types of fuse/relay setups.

Trouble shooting reveals no power to the brown wire which powers the running lights. All other systems are go with no wire breaks/grounds/corrosion or physical maladies. All fuses are ok both by visual inspection and on an Ohm meter. I even pulled the lower driver's side panel and wormed myself into a place where I could look at the BCM box. My truck installation does not have any relays or fuses in this area, only in the IPDM and fuse panel adjacent to the glove box.

I do have a three-relay trailer power installation in a weather resistant box installed just in front of the IPDM. It contains two blue turn signal relays and one brown master, all factory installed and well marked. They are powered and work just fine in the truck and on a test bench. They just don't send power to the Brown wire at the hitch plug (or at the coupler plug up inside the frame).

Question: Since many, many posts on this very problem refer to an OEM aftermarket relay installation installed behind the passenger side cab kick panel, (which I do not have installed), is this set also required in addition to the engine space installation? I ask as I have found a schematic for trailer power on the internet that shows two master relays and two turn signal relays.

Any ideas? Thanks.
 

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pep boys sells a tester for about $5 that plugs in to your 4 pin to test the truck side wiring.

Clint
 

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The harness installed in front of the ipdm is factory, and part of the BDM system for your TRUCKS turn signals/tail lamps/brake lights. If your're missing the Y-harness and relays under the passenger side kick panel, that's your problem. These parts are required for the factory wiring to supply voltage to the harness leading to the back end of the truck. Check the thread in my signature for part numbers and installation pictures.

You can get the entire factory kit for like 67$ which contains all the parts needed for a 7pin. Then you can get a 7 to 4 pin adapter for 4 wire trailers. OR, splice in for what you need downstream of the factory connectors on the frame rail once you get the y-harness and relays listed in my thread. This is a common problem I read all the time. Thus my making the thread. Perhaps it should be a STICKY?!
 

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Discussion Starter · #4 ·
Hopefully this will make it happen!

Thanks to both replies.

I have a pocket tester on order. I have a pretty good electrical/electronics background and ran the circuit down with a multi meter but this required a lot of crawling and climbing in cold, wet weather.

Many thanks for the final piece of the puzzle about the need for an additional harness and relays (behind the kick panel). No one else has made this obvious. One would think that if you find a set of relays factory installed and a 4-pin lead at the tail end then you would have a "factory installed tow package" that is ready to hook up a trailer and drive away.

I'll order the other components today and install them. I'll be glad to report back so that any future frustrated DIY's will zip right to the issue.
 

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Discussion Starter · #5 ·
Trailer light issue solved

Hopefully this post will aid anyone facing the same problem: Trailer running lights not working while brake and turn signals illuminate correctly.

My '07 "appeared" to be factory wired for a 4-pin trailer connection. The first time I plugged the trailer to the vehicle I had the head-scratching moment many others have encountered. No running lights.

A thorough search of the internet brought me to this forum and some, "almost answered" threads. It appeared that I needed to install yet another set of relays (one 'brown' master and two 'blue' turn signal relays) behind the kick panel on the passenger side.

Thanks to some great product pointing by senior posters here, I got the installation for about $65 on Amazon. The kit includes everything you'll need for a 7-pin installation. For now I don't need that and just left the plug and whip in the box and installed the new relay harness. Ten minutes of work. I'm in business.

In summation: If it looks like a duck, walks like a duck but won't light up like a duck - you are almost there but you'll need relays both under the hood and in the cab. I wish I could explain the logic, but only know that the two sets complement one another.

Thanks to all for the guiding advice.
 

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I had a similar problem. My trailer sat for a pit and one pin of the trailers wiring was dirty/rusty. I took a wire brush to it and cleaned it up. It work perfect afterwards
 

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Truck: '07 Crew Cab XE - standard transmission, 4 pin lighting system.

Issue: new trailer (to this truck), brake and turn signals are fine but no running lights. Trailer lighting installation is just fine, works like a champ on other vehicles and from a stand alone battery.


Research: This forum and others seem to point problem areas, a) fuses/fusible links, b) installed relay systems vary widely, c) the usual broken wires, loose or corroded connections etc.

Forums and discussions seem to indicate that while there are number of commonalities, there are a number of different types of fuse/relay setups.

Trouble shooting reveals no power to the brown wire which powers the running lights. All other systems are go with no wire breaks/grounds/corrosion or physical maladies. All fuses are ok both by visual inspection and on an Ohm meter. I even pulled the lower driver's side panel and wormed myself into a place where I could look at the BCM box. My truck installation does not have any relays or fuses in this area, only in the IPDM and fuse panel adjacent to the glove box.

I do have a three-relay trailer power installation in a weather resistant box installed just in front of the IPDM. It contains two blue turn signal relays and one brown master, all factory installed and well marked. They are powered and work just fine in the truck and on a test bench. They just don't send power to the Brown wire at the hitch plug (or at the coupler plug up inside the frame).

Question: Since many, many posts on this very problem refer to an OEM aftermarket relay installation installed behind the passenger side cab kick panel, (which I do not have installed), is this set also required in addition to the engine space installation? I ask as I have found a schematic for trailer power on the internet that shows two master relays and two turn signal relays.

Any ideas? Thanks.
Check the fuses in the relay box under the hood. The relay box is the smaller of two boxes on the passenger side. There are 3 fuses beside the relays that control the directional lights and brake lights. This solved my problem having running lights ,but no left or right turn signal or brake lights on my trailer.
 

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I had the same problem on my 2016...turns out Nissan only installed one of the blue relays under the kick panel on the passenger side. How it left the factory that way I'll never know.
 

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Will I need to purchase the CURT 56225 fuse harness to install the fuses inside the cab by the passengers side to get my trailer running lights to work along with my cruse control. All other lights work fine.
 

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Still no running lights to trailer. No power on brown wire. Everything else works. Ordered wire harness adapter and the three relays ( 2-Blue and 1-Brown) to install inside passengers side to see if this will solve the issue. All other fuses checked and all good. Truck came with a ready trailer connection and trailer connection was bought from dealer. Next step if does not work will have to take to the dealer. I do have two blue and one brown relay under the hood in the fuse box. and the small fuse was also checked. Not happy with my first Nissan Frontier at this time!
 

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Still no running lights to trailer. No power on brown wire. Everything else works. Ordered wire harness adapter and the three relays ( 2-Blue and 1-Brown) to install inside passengers side to see if this will solve the issue. All other fuses checked and all good. Truck came with a ready trailer connection and trailer connection was bought from dealer. Next step if does not work will have to take to the dealer. I do have two blue and one brown relay under the hood in the fuse box. and the small fuse was also checked. Not happy with my first Nissan Frontier at this time!
Just wait until you find out they switched the aux power and the brakes on the 7 pin. Not on all frontiers but a surprising amount will lock the brakes up as soon as you plug in your trailer. Not sure why but they never really fixed the issue.

 

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Just wait until you find out they switched the aux power and the brakes on the 7 pin. Not on all frontiers but a surprising amount will lock the brakes up as soon as you plug in your trailer. Not sure why but they never really fixed the issue.

Yupper. My 2014 Pro4 was flipped, plugged in a 7-pin tester to confirm. Reversed wires as directed, all is well.
 

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2020 frontier king cab 4x4
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after many years of playing around with trailer wires, mostly 4 pin, I have concluded that bad grounding of the trailer lights is 90% of the problem
 

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I have all of the correct wiring and relays. I added them when I bought my truck. When towing my cargo trailer the running lights just stopped working at night so I immediately knew they went out. I verified everything is connected good and no fuses are blown. Has anyone ever had a relay go bad? Towed the trailer a dozen times over a year and never had an issue. Based on what I have read here I will find the ground wire on the trailer and verify it is good.
 

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I have all of the correct wiring and relays. I added them when I bought my truck. When towing my cargo trailer the running lights just stopped working at night so I immediately knew they went out. I verified everything is connected good and no fuses are blown. Has anyone ever had a relay go bad? Towed the trailer a dozen times over a year and never had an issue. Based on what I have read here I will find the ground wire on the trailer and verify it is good.
Relay failures on reputable relay brands are exceedingly rare. I'd concentrate on trailer grounds, get a 7 ping tester and plug it in, see what's what in seconds.
 

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Relay failures on reputable relay brands are exceedingly rare. I'd concentrate on trailer grounds, get a 7 ping tester and plug it in, see what's what in seconds.
Thanks I have narrowed it down to fuse F4 in the larger box under the hood. Every time I plug the 7 to 4 pin adapter in it blows. I bought a new adapter and the same thing happens. I am going to replace the 7 pin receptacle on my hitch with a new trailer tow harness from the frame to the hitch and see if that fixes the issue.
 

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2018 Frontier 2wd king cab
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I had brake lights and turn signals I added the 999t8-br004 harness for running lights. The right brake light stayed on at all times the only way to kill it was unplugging the trailer pigtail. So I removed the harness I don't tow at night anyway. But now I don't have any lights at all? The f4 trailer fuse is not blown either?
 

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And what some don't tell you is 2 blue relays for the manual transmission, and only 1 Blue relay for the automatic transmission. See post #14
 

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And what some don't tell you is 2 blue relays for the manual transmission, and only 1 Blue relay for the automatic transmission. See post #14
This is correct, basically, plugging in the second relay on an A/T will not harm anything, it just doesn't do anything. My Tekonsha kit came w/ three and I plugged 'em all on, that way I don't have to guess if I left out the correct socket. Works just fine.
 
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