Can NOT get trailer lights to work

[tstex]

@tstex

The parts guy at Tasca is sort of correct.... I believe the harness has 5 or 6 direct connect plugs on it... (see pic below)... I believe 2 connect on the right rear & 2 on the left rear near the tail connections on the harness... The others 1 or 2 connect to the truck harness on the frame (I believe one is power & the other is for the fuses & brake controller.... but don't hold me to that)

It is not a very long harness all connections should be at the rear of the truck... when you get the new one & lay it out it is pretty straight forward. I installed one on my brothers truck yrs back... so I'm going on memory...


View attachment 731316

Thanks again, dlc ! the A part number is much, much shorter than the B part #. the B one looks like intestines bc it has so many diff wires...If you have installed in on a F-150 before and all is good, then I will go w that, order and then post back if I need help. if I knew the total length of the harness, I could just work backwards from where the receptacle goes in to see where the 4-pin rectangular plug goes.

Finally, another challenge I am going to have is "rounding out the hole" in the bracket where the 7-4 pin receptacle goes. When my back end hit the ground/street, it made the round hole oblong. The round portion of the receptacle was also "oblonged" and made it impossibe to install the 7-pin adapter. I am going to have to "re-round" it out w a round rat-tail file or similar. Once it's good, I am going to tape-off the area and spray paint it black w 4-5 coats. That bracket is welded on there pretty good so I am not going to remove it unless it's imperative.....thanks again !

 

[pmsmechanic]

What I did on my trucks is move all the trailer plugs inside the box. That way I have no more issues with corrosion from road salt and gravel beating everything to pieces. A short trailer extension cord and I can hook onto my trailers without issues and I haven't repaired a trailer plug of my own for years.

 

[sandytrail]

My 2003 Ford F250 was acting the same way with my trailer. I eventually discovered the problem was with a connector under the rear of the truck. That is where the pigtails that go to the trailer connectors on or near the back bumper connect to the main power going to all the trailer connectors. That connector was loose and I pushed it back together and everything worked. Just a thought.

 

[Dftodd]

At the risk of exposing myself (as incompetent in wiring)...

I recently went to sell a dump trailer. The plug wiring had been chewed off by my dog a couple years prior and I'd wired a new one in its place. As I never used this trailer on the road (just on-farm, behind a tractor) I had never tested it. And wouldn't you know it, I went to test it out hooked up to my truck only to find out that I didn't have lights (some, but they were all messed up). Checked all the wiring on the trailer and all checked out. Verified that the plug was wired up correctly (7 pin). Was totally stumped as my utility trailer worked when hooked up to my truck. After more time than I'd like to admit, I finally figured that I'd wired the receptacle (truck) incorrectly (years ago). And if you're following along you'll understand that this means that my utility trailer is ALSO incorrectly wired (still on my TODO list).

Don't assume that plugs and receptacles are wired correctly. From one perspective they can appear to be, but it's easy to get flipped when looking at schematics and then reversing things as you wire into the back side.

There are wire color changes going from a four flat to a 7 pin rv plug that is standard on most trucks.

The yellow wire on a 4 flat is left turn, green is right turn, brown is parking lights.

Once you get up to the 7 pin, yellow is aux power, brown is right turn, green is parking lights, red is actually for left turn.

What many people make mistakes with (me included) is when someone is used to wiring up 4 flat plugs all the time.

If you convert a trailer thats wired for a 4 flat to a 7 pin and hook color for color the lights start acting really trippy left brake light will stay on all the time. Parking lights turn on the right turn signal. And right turn will flash both parking lights.

And your sitting there wondering what the F is going on with your blasted trailer lights

Every newbie mechanic I get through my shop runs into this issue the first time they install a 7 pin rv plug on trailer wired for a 4 flat

 

[newbury]

My 2003 Ford F250 was acting the same way with my trailer. I eventually discovered the problem was with a connector under the rear of the truck. That is where the pigtails that go to the trailer connectors on or near the back bumper connect to the main power going to all the trailer connectors. That connector was loose and I pushed it back together and everything worked. Just a thought.

I had a similar frustrating problem with me F350. The truck side of the trailer was "flaky". All lights and brakes would work. Then they might not. Traced it down to the plug in the truck had a corroded connection inside. When pushed hard together (like when plugging in a 7 pin tester), all worked. With the trailer wired up it might not.
Replaced the plug.

 

[DieselBound]

There are wire color changes going from a four flat to a 7 pin rv plug that is standard on most trucks.

The yellow wire on a 4 flat is left turn, green is right turn, brown is parking lights.

Once you get up to the 7 pin, yellow is aux power, brown is right turn, green is parking lights, red is actually for left turn.

What many people make mistakes with (me included) is when someone is used to wiring up 4 flat plugs all the time.

If you convert a trailer thats wired for a 4 flat to a 7 pin and hook color for color the lights start acting really trippy left brake light will stay on all the time. Parking lights turn on the right turn signal. And right turn will flash both parking lights.

And your sitting there wondering what the F is going on with your blasted trailer lights

Every newbie mechanic I get through my shop runs into this issue the first time they install a 7 pin rv plug on trailer wired for a 4 flat

My issue wasn't with changing plug types, but with replacing plugs. Looking at a schematic from the front and then wiring at that back- it's easy to get reversed/flipped. I suppose with a four-pin it's not an issue (flat). A note, however, is to not assume that something is wired correctly in the first place: whoever wired up my truck before me had one hack of a mess (and then someone installed an aftermarket security system and what I found under the dash area was as repulsive of a job as I've ever seen- was running wiring for a new brake controller and was forced to clean things up because I couldn't button things back up in such disorder).

 

[Dftodd]

My issue wasn't with changing plug types, but with replacing plugs. Looking at a schematic from the front and then wiring at that back- it's easy to get reversed/flipped. I suppose with a four-pin it's not an issue (flat). A note, however, is to not assume that something is wired correctly in the first place: whoever wired up my truck before me had one hack of a mess (and then someone installed an aftermarket security system and what I found under the dash area was as repulsive of a job as I've ever seen- was running wiring for a new brake controller and was forced to clean things up because I couldn't button things back up in such disorder).

I was tracing out some trailer light issues on a piece of equipment that had just been shipped in from another location.

I soon came to the conclusion that the person was dyslexic and color blind

Plug was wired completely wrong. Then there were several places in the wiring where they had cut and spliced wires back together. One splice had a green wire hooked to brown. Then yellow was hooked to green, and then they managed to hook the brakes to the turn signals

I came to the conclusion pretty quickly that it would be cheaper and faster just to replace the wiring.

 

[Bearsixty7]

There are wire color changes going from a four flat to a 7 pin rv plug that is standard on most trucks.

The yellow wire on a 4 flat is left turn, green is right turn, brown is parking lights.

Once you get up to the 7 pin, yellow is aux power, brown is right turn, green is parking lights, red is actually for left turn.

WHAT?? What year and model because most 7 way 's have used the same convention as the 4 ways for many years, they just add 3 more,

Aux is Red
Brakes is blue
Backup lights is center pin, usually light green

Many examples of this on the web.

 

[Dftodd]

WHAT?? What year and model because most 7 way 's have used the same convention as the 4 ways for many years, they just add 3 more,

Aux is Red
Brakes is blue
Backup lights is center pin, usually light green

Many examples of this on the web.

Might wanna pick up a 7 pin rv plug from the local parts store that is labeled for color and try it out.

You'll find the diagram you posted is incorrect. Functions labeled in your diagram are correct. The colors are wrong though.

Not sure on the vehicle side. All I test for is function there when diagnosing a trailer issue.

On the trailer side, blue and white are correct. Yellow is labeled as the center plug for aux power. Black is back up lights, red is right turn, brown is left turn, green is right turn.

I haven't seen a replacement 7 pin rv plug thats been labeled for function in about 6 years. They've come labeled for color and wire up as I stated above.

I just replaced two of those plugs today on equipment at work.

I take a plug apart Monday and post a picture.

 

[DieselBound]

WHAT?? What year and model because most 7 way 's have used the same convention as the 4 ways for many years, they just add 3 more,

Aux is Red
Brakes is blue
Backup lights is center pin, usually light green

Many examples of this on the web.

NOT flat pin: I was wiring up plugs and receptacles. And, as I stated in my original posting, I'm not a wiring genius (BUT, I'll at least not make a rats nest out of things ). Just thought that I couldn't be the only one who has gotten things backward: wasn't born knowing these things.

 

[Bearsixty7]

Might wanna pick up a 7 pin rv plug from the local parts store that is labeled for color and try it out.

You'll find the diagram you posted is incorrect. Functions labeled in your diagram are correct. The colors are wrong though.

Not sure on the vehicle side. All I test for is function there when diagnosing a trailer issue.

On the trailer side, blue and white are correct. Yellow is labeled as the center plug for aux power. Black is back up lights, red is right turn, brown is left turn, green is right turn.

I haven't seen a replacement 7 pin rv plug thats been labeled for function in about 6 years. They've come labeled for color and wire up as I stated above.

I just replaced two of those plugs today on equipment at work.

I take a plug apart Monday and post a picture.

Oh, you said "There are wire color changes going from a four flat to a 7 pin rv plug that is standard on most trucks.
The yellow wire on a 4 flat is left turn, green is right turn, brown is parking lights. Once you get up to the 7 pin, yellow is aux power, brown is right turn, green is parking lights, red is actually for left turn."

So I thought you meant the trucks were wired differently.
As far as I know most trucks have used this color scheme for years and that is what I was referring to.
Trailers, well who knows, You would think that trailer manufacturers would follow suit (and some day they will) but we all probably have encountered trailers that were wired weird and a nightmare to correct.

 

[pmsmechanic]

but we all probably have encountered trailers that were wired weird and a nightmare to correct.

I once worked on a stock trailer that had the wiring inside in one of the frame tubes running front to rear. Inside the tube was a splice and a wiring color change at the splice. Grrrrr!

 

[tstex]

Here's an out of the box question for those that have been following this thread, but w one note prior to ques. It's apparent on the F-150 and other trucks that have the trailer receptacle so low, has been hit, pelted and water soaked under flooded conditions. That's probably the case w mine bc we sometimes get 5-10" rains and the streets are flooded.

With that thought in mind, has anyone ever tried relocating the receptacle to higher up on the bumper, like near the license plate lights? At least it would not get smashed or hit w water as much. Not sure about rain when parked outside, how that might impact the plug. Since the bumper is basically hard plastic in that area, I could buy another bracket and install...then it's plug'n'play. Thoughts ??

 

[Norm W]

Being color crippled everything is done with a test light. I don't care what color the wires are. Many times I think the manufacturers use what ever color they have handy. If the wires are live when the appropriate light is turned on it is marked with numbered tape. The usual problem with trailers is bad grounds. I always run a separate ground wire.

 

[dodge man]

Not a great picture, it of the lights I added to a bike rack, but if you look closely you can see the trailer lights plug in to the left of the license plate. It’s that way from the factory.

 

[RandyT]

Being color crippled everything is done with a test light. I don't care what color the wires are. Many times I think the manufacturers use what ever color they have handy. If the wires are live when the appropriate light is turned on it is marked with numbered tape. The usual problem with trailers is bad grounds. I always run a separate ground wire.

Agree on the separate ground. Every trailer that I have wired I run a separate ground wire and connect to each light. and then connect everything to the trailer plug. I don't use the trailer frame to ground anything on the trailer.

 

[Dftodd]

Here's an out of the box question for those that have been following this thread, but w one note prior to ques. It's apparent on the F-150 and other trucks that have the trailer receptacle so low, has been hit, pelted and water soaked under flooded conditions. That's probably the case w mine bc we sometimes get 5-10" rains and the streets are flooded.

With that thought in mind, has anyone ever tried relocating the receptacle to higher up on the bumper, like near the license plate lights? At least it would not get smashed or hit w water as much. Not sure about rain when parked outside, how that might impact the plug. Since the bumper is basically hard plastic in that area, I could buy another bracket and install...then it's plug'n'play. Thoughts ??

Mine is mounted stock next to the tag on my Sierra so it's protected.

I'm on my second replacement on my service truck. First time it shorted out in a quarry. Had to go through 3'ft of water to get to the equipment I was working on.

Second time was last week. There was a frame recall on the truck. They had to pull the bed and crane to add support rails behind the cab.

Tech snapped a couple pins in the quick connect when he hooked it back up.

I saved the old one so I can show the service manager at the dealership. His shop foreman needs to get more pictures so they can get paid for the recall. So I'm gonna swing by Monday. I'll bring it to there attention then.

 

[Dftodd]

Agree on the separate ground. Every trailer that I have wired I run a separate ground wire and connect to each light. and then connect everything to the trailer plug. I don't use the trailer frame to ground anything on the trailer.

Boss had a small tilt trailer that he couldn't get the lights working on. He replaced the ground wire and hooked it to the tongue. Cleaned the connection for the ground on the lights.

I pointed out that he needed to run a jumper wire from where he hooked the ground to the tongue, to the frame where his lights attached he didn't take unto account for the loss of connection where it pivots.

 

[RandyT]

Boss had a small tilt trailer that he couldn't get the lights working on. He replaced the ground wire and hooked it to the tongue. Cleaned the connection for the ground on the lights.

I pointed out that he needed to run a jumper wire from where he hooked the ground to the tongue, to the frame where his lights attached he didn't take unto account for the loss of connection where it pivots.

Sounds like another case of somebody thinking that the trailer is supposed to be grounded through the trailer ball back to the tow vehicle instead of through the trailer wiring harness back to the wiring harness on the tow vehicle and then connected to the vehicle frame or negative battery terminal.

 

[Dftodd]

Sounds like another case of somebody thinking that the trailer is supposed to be grounded through the trailer ball back to the tow vehicle instead of through the trailer wiring harness back to the wiring harness on the tow vehicle and then connected to the vehicle frame or negative battery terminal.

He actually ran a ground to the tongue. What got him was his lights were mounted to the portion of the trailer that pivoted. he didn't take that into account.