I have a 2005 F150. Here's my problem, I don't have any power going to the trailer hookups(neither the 7 or 4 pin) to power the running lights but have everything else. I took my test light and checked right behind where the harness that goes to the plug in hooks up to the main harness and got nothing. I then checked above the connection on the main harness and had power so I assumed there was a broken wire somewhere along the harness going to the plug ins. I took all the wire looms off and everything looked fine so I decided to swap the wiring harness out with the one on my wifes truck(hers worked). Well, the harness that came off my truck works fine on hers and hers doesn't work on mine.

I checked the wire above the connection again and it had power so I figured there was something wrong with the portion of the connector that powers the running lights so I cut the wire loose from each end of the connector and ran a jumper wire. Now I have power going through the jumper wire and into the harness that goes to the plug ins but I still have no power at the plug ins. What is going on here?

And to make things worse now I've compromsed the wiring harness and if the wire I spliced into fails for any reason I loose all power to the rear lights of the truck as well as the trailer.


I wonder now if I should just cut every wire loose and redo the entire thing, totally bypassing the connector.

 

Is this trailer plug/harness factory? If so, I think you are getting the truck's lighting wires mixed up with the trailer harness wiring, they are two different things if you have the factory tow plug/harness.

If you do not have the factory tow plug/harness, then you have a "tee" that someone bought and plugged into the truck's rear harness, and the trailer does use the truck's lights for the trailer.

If you have the factory setup, I would put everything back, and look up front in the fuse box for a trailer running lights fuse. If you have enough wire, I would repair the wiring by using solder, and then get some of that paint-on tape and paint the solder joint to repair the wire, or when you go to Radio Shack to the get the soldering iron and the solder, you could also get some shrink wrap to cover the wires.

 

Franklin, everything is factory. I'll check for a bad fuse, but I was wondering how come I havepower going through the splice and into the begining of the harness that goes to the plug ins but it doesn't make it all the way to the end? Would a bad license plate marker cause a short in the system? I noticed one of them wasn't working.

Also, somehow the trailer light plug in and the rear lights on the truck are tied into each other. when I unplug the harness connections that goes to the plug ins or unhook the ground for the harness the taillights go out too. There is a second connector that is off to the side and I think that might be the link that sends power to the truck lights.

 

A couple things come to mind. And they may not prove to be the solution but perhaps worth considering anyway.

Since the rear harness section (for the trailer plug-ins) seems to work on the wife's truck, but not your's... then you may reasonably assume (for the time being) that the individual wire which is supposed to supply power for the running lights on your trailer harness section is ok. And since you've bypassed the first connector (on the main harness end) then that leaves two plausible possibilities;

1) Something's wrong at the trailer-plug connection; or..

2)Something's possibly amiss with your testing procedure.

My first thought is to double-check your trailer plug connections.

If all trailer plug connections appear to be sound -- Then double-check your testing procedure again to make sure you've verified every mental assumption with a 'proven' actual testing result.

For example: After connecting the trailer harness-section up again -- when you 'check' for power at the trailer plug with your test light... are you clipping your test light's alligator-clip to a verified good (and clean) solid frame ground point for the test? -- or are you testing the circuit by connecting the test light's clip to an (assumed) return path such as a ground wire within the trailer plug itself?

Often times the problem isn't so much with the incoming 12V power side - but with the circuit's return-loop path (sometimes called the ground side of the circuit). Partial or open ground connections are often mistakenly assumed to be good.. and when used for 'testing' a circuit can easily be misinterpreted as being a problem with the power input side.

hope that helps
dave

 

problem solved. there was a blown fuse on the panel in the cab. I feel like an idiot now, I thought about checking the fuses last night but I figured if there was power going to the harness that the fuses had to be ok. i wish I would've looked at the fuses first before I spent an hour testing everything and then cutting and splicing wires.

 

just look at this way... now you've got a more refined trouble-shooting plan for the next time, and you've also gained helpful knowledge for that buddy who's bound to run into the same problem sometime down the road.

glad you got it solved.

 

I have a 2005 F-150 just bought some tailgate LED lights that mount under the tailgate and hook into my trailer harness plug. Mounted them and the work as long as I don't cut on my lights or parking lights. When I cut on my lights and turn on my left turn signal it stays on but does not blink then try the right side and it blinks slow. Also the hazards will not work either when the lights are on. If I cut off the lights the blinkers and hazards work. I have seen several other posts that people have about the same problem when they hook up to a trailer but have not seen a answer. I checked the fuses except for #9 the park lamp relay or the relays. Could this be a bad ground in the harness and how could I check this out.

 

It sounds like a bad ground. But I would suspect the new lights or the trailer plug wiring on the light side. See how the new lights are grounded. Are they grounded through the body or are they grounded through the trailer plug?

 

Yes, there's a possibility that you have a faulty return-path (insufficient ground) somewhere in the circuit.

Do you have a properly wired trailer you can hook up to... to verify good wiring (and actual operation) of the trailer harness? [**hint: the metal-to-metal physical contact {trailer coupler-to-trailer ball hookup} - IS NOT the proper electrical grounding return-path for trailer lighting.

-- if so (and the trailer lights seem to work properly) then look to the possibility that the LED lights might have accidentally been mis-wired into the trailer connector (on the LED side). -- also double-check to verify that all the pins of two halves of the trailer connector are making a solid good connection.

Trailer lights (and vehicle lights) typically use *double-filament* bulbs.. that means the signal & brake lights assemblies employ two different power-side circuits. -- It's very common to find an accidental "cross-wiring" of these control wires -- which can cause similar symptoms as you describe.

- But double-check for all good grounding points/wires first. Chances are pretty good that's where your problem lies.

 

It's not grounded by the light it self because it is a strip of plastic with the LED's so it has to be grounded gy the 4 pin harness could I just put a ground wire to the plug and try and plug it back in. Because everything works properly when the lights are off so the Im wondering which pin would give power to the parking lights or running lights. Should I splice into the harness on the light side and just go directly to a ground on the body of the truck?

 

The ground pin on a standard 4-pin trailer connector setup is always the "odd" pin on the connector (either side). It's a male pin on the vehicle side and a female socket on the trailer side. Standard color-code of the ground wire is 'white'.

Standard color-coding for the parking/running lights wire is: 'brown'
Yellow wire = Left signal/brake Green= Right signal/brake

If it were me, I'd first verify whether or not you have a good ground on the vehicle side of the plug. If your connecter wires were 'patched' into the vehicle's wiring at some point in the past..then that's a likely spot to check for corrosion.... typically at the splice point. If you still have the same problem after verifying all good grounding connections... then you most likely have a crossed connection between one of the Green/Yellow wires and the brown wire.

You must use a good 'test-light' for testing the above... because just using the 'continuity' function on a DMM won't actually test the circuit under enough load to give a reliable indication.

 

Thanks for the help I went out and tried another ground and this time the right turn signal did not work. So I took the harness onthe light and tried like you said and crossed the 2 wires that were labeled for turn signals and it ended up switching the 2. So now I ended up with opposite turn signals so I knew that it was not it so I disconnected the other wire on the light harness that was labeled + . So at this point I have a turn signal wire for both sides and the ground wire plugged into my harness on the truck and this fixed the problem now I can turn on my lights and everything works. But I still don't know if it will work on a trailer because I eliminated the brown wire on the harness which is the parking lights. I checked all the fuses and they are good so it still could be the relay or that brown wire from what I understand is it is always hot and it goes to to the tow trailer parking light relay. I found a wiring diagram on here and it pointed that is where the brown wire goes. Well it was a rough time figuring all these scenarios out and I really appreciate all your help. I hope there is a answer out there for the people who are hooking up trailers if you come up with one please let me know. Thanks.

 

Are these LED lights supposed to light when the running lights are on? If they only have two wires, I don't think they have that function built into them. You need 3 connections for all the taillight functions, 1 wire for brake/turn, 1 wire for running lights, and 1 wire for a ground.

 

Don't know if they are supposed to be on with running lights what ever that + wire on the light harness was for it was back feeding or something through my brown wire on truck harness to make it not work properly when I had my lights on. These lights did not have directions ot was suppossed to be plug and play. I still could have something wrong with my truck plug whatever that brown wire goes to I think it is that relay. But I don't have a trailer to hook up to. I might try to find a trailer in the next couple of days just to see so I could narrow it down. But at least I have all my lights working now. If I find out I will post just to help out others with this problem it is aggrevating.Thanks.

 

The brown is the running lights. That's why I asked the previous question. Right brake/turn is green, left brake/turn is yellow, ground is white.