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Lou P.
Lou P., ASE Certified Technician
Category: Ford
Satisfied Customers: 3948
Experience:  Have been working on Ford GM and Chrysler for 15+ years and ASE master certified.
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Ford F150: Just bought a plug in trailer harness F150.

Customer Question

Just bought a plug in trailer harness for 2001 F150. Hooked up and right brake and turn light will not work. Ground is clean and good. Fuses are good too. Anyway to trouble shoot?
Submitted: 1 year ago.
Category: Ford
Expert:  Lou P. replied 1 year ago.
Hello my name is ***** ***** i will do my best to help you , i strive for EXCELLENT service and nothing more. May I ask for some more clarification ?
Is it the lights on the trailer that is the issue ? Or the truck ? And if it is the truck, do they work fine when you unplugged the harmed and put it back without the trailer wiring ?
Customer: replied 1 year ago.
On the truck. Bought a plug in harness no splicing or wire cutting. All lights work with light tester except right brake and turn signal. Trailer is not hooked up. I have sanded and cleaned area for grounding. I checked fuses inside and under hood all look fine. All connectors good. can you please list fuses + amps to check? Pics attached. Please help!
Expert:  Lou P. replied 1 year ago.
Ok now what if you remove the trailer wiring and plug the truck wiring back together ? Try that.
Also is it just the brake and turn? Or is it the running lamps also ? What about reverse ? And can you put the hazards on and see if they work on both sides in the rear. All of those answers to my questions will tell me what your issue is. So please try them all in order and respond with answers to all of them. Thanks !!
Expert:  Lou P. replied 1 year ago.
I did not mean to send that last message as a "answer" please ignore , but do reply with the results.
Customer: replied 1 year ago.
Yes when harness is unhooked all lights work. Running, reverse and hazards. Only thing not working is trailer hookup right signal and brake. Could it be a fuse? Could you please send list of fuses to check along with amp for fuses.
Expert:  Lou P. replied 1 year ago.
It will not be a fuse as the same fuse works the stop lights in the truck. So if the truck is working then the trailer should be working.
So how many lights are on the right side of your trailer ?
Expert:  Lou P. replied 1 year ago.
Also are you working with a 7 pin trailer harness ? Give me the part number of your harness please. You may have a faulty harness.
So to be clear everything works on the truck. Your issue is with the trailer connector not getting the correct power at the right turn signal pin? And when connected to the trailer it doesn't work the right stop or turn ?
Customer: replied 1 year ago.
It's not the trailer it is the 4 pin connector from truck. When testing right brake and turn signal do not work. Not testing with trailer I'm using a brand new light up tester. Running lights good , left turn and brake good. All truck lights work. Only right turn and brake for trailer hookup not working.
Expert:  Lou P. replied 1 year ago.
Ok perfect thank. Clarification is the hardest when working over messaging like this. Ok then you are working with the green wire on the connector yes?
Expert:  Lou P. replied 1 year ago.
We need to poke the green wire at the back of the trailer connector and then poke it at the T connector up under the bed to see if the light is even getting a signal right at the vehicle plug in and if the power is making it to the back of the trailer plug. I have also sent a offer for live chat. This may be way easier over the phone. Up to you. Lou
Customer: replied 1 year ago.
What do you mean by poke?
Expert:  Lou P. replied 1 year ago.
Ok if you have a test light then the tip should be super pointy , so wth the test light wire on the trucks "ground" you should turn on the turn signal and poke through the wire insulator and pierce the wire , if the truck works fine then the fault is with the trailer wiring harness. I really think to save time you should return it and get another one.
That's makes the best sense. The truck supplies the same signal to the trailer harness as the rear taillights so all the harness does for the trailer is splice into the trucks harness. So if the truck works and the trailer plug doesn't then the fault is with the trailer wiring kit. After going over that in my mind , don't bother waistband any more time testing until you change that trailer plug adapter harness wth a new one. And make sure you read the package and it labels the correct wiring just to be sure. The terminals should be
White = ground
Red = taillights
Yellow = left turn
Green = right turn.
I really believe that if all those are correct then you need a new harness. Return it and get another one. Only then can we really trouble shoot.
I have taken my time to answer your question the best i could and i will continue to help if you need follow up information , all i ask is that you PLEASE take a second to rate my service so i may recieve my credit for assisting you. Thank you.
Customer: replied 1 year ago.
This is my second harness.
Expert:  Lou P. replied 1 year ago.
Well that took the wind out of my sails.
Ok then. This does not make sense. What is the part number you have for the trailer wiring. I need that.
It's as simple as this. If the truck works then plugging in the adapter harness for the trailer will work.
So give me the part number to your harness please
Customer: replied 1 year ago.
BK(###) ###-####from napa
Expert:  Lou P. replied 1 year ago.
Ok I will check that. Also have you attempted to hook up a trailer ? If so when you turn the right signal on does the tuck flash fast like a bulb is out or does it not flash at all ?
Customer: replied 1 year ago.
Nothing happens just like tester.
Expert:  Lou P. replied 1 year ago.
Ok now what if you connect the truck back together like normal without the trailer wiring and function the lights. I don't care if they worked before I'm interested in if they will work now. Can you try that ?
Customer: replied 1 year ago.
Yes lights work as normal when harness is unhooked. I thought maybe an under powered fuse might effect? I wanted to verify proper fuses (number on fuse) to make sure lights getting proper power. Would that effect anything?
Expert:  Lou P. replied 1 year ago.
No the fuse either works or does not. Ok with two harnesses tried then it's possible that the problem is the turn signal switch.
The switch is what all the power passes through. That why I asked you to try the hazards. And you never answered me if they work or not. If the hazards work then the circuit is GOOD and the problem is the turn signal switch assembly also called the multifunction switch. Can you try the hazards for me ? And test for power at the connector of the trailer plug or simply plug in the trailer and see if they come on. ??
Expert:  Lou P. replied 1 year ago.
Also if your truck has the trailer wiring option then there should be a plug just hanging back there somewhere and you should have used part number
BK(###) ###-####
My factory diagram shows a plug specific for the trailer harness. But if you had to add a hitch yourself then the wiring is probably not there.
Customer: replied 1 year ago.
Sorry, hazards do not work on right side of trailer hookup either. hazards work fine on truck with and without harness. i do not see any loose plugs. can you please specify where that would be? how many questions am i able to ask for the $38.00?
Expert:  Lou P. replied 1 year ago.
As far as the fee we are good on this until you are happy with my service. So even though you paid the deposit. I do not get paid until you rate me positive. And I am ok with not being rated until we solve your issue.
Back to the lights. So you are saying that the hazards work fine with the trailer connected but only on the truck. Not the trailer.
And you said that the turn signals do not work on the truck or trailer with the trailer connected or also with just the trailer wiring connected ?
Also I sent you a service offer to speak over the phone , are you not interested in that ?
Customer: replied 1 year ago.
yes, they work on truck with trailer connected and not connected, and the left hazard, signal and brake will work on trailer. no right hazard, turn or brake.
Expert:  Lou P. replied 1 year ago.
ok. If the truck works as far as ALL the lighting no matter if the wiring is hooked up or not. And you are being truthful about this being the second harness. We may have a issue where the harness is mis manufactured. I'm running through all of the scenarios. And the problem is not with the truck. It's with the trailer connector.
Let me see if I can find a good diagram of that trailer plug.
Customer: replied 1 year ago.
yes second harness lol. that was my first thought too. i know these trailer light issues can be tricky for sure.
Expert:  Lou P. replied 1 year ago.
Ok here's the last thing to try. At the truck end of the connector for the factory wiring. Turn on the turn signals and poke the test ligt through the Orange wire with the stripe I was telling you about. The test light should now flash with the turn signals. If it does. Then poke through the green wire right at the connector on the trialer harness right there up under the bed where you tested the Orange wire. If there is no flash then the trailer adapter is the problem. Try once from autozone. Part number 40145 made by Hopkins , hopefully it's not the same company just repackaged. That is it man.
If the truck works no matter what is plugged or unplugged and there is no power at the turn signal pin on the trailer plug then the issue is with the trialer harness. If need be you can just buy a 4 pin with long wiring and I can tell you how to splice it into the factory harness.
I can't tell you what is wrong with the connections you have but if it was something with the lift circuit the turn signal would be affected while the trailer was hooked up or the turn signals activated. It would flash fast or not at all or something would be affected. So if the truck works fine no matter what then the issue is with the trailer harness. That is the ONLY thing that makes sense electrically.
I have taken my time to answer your question the best i could and i will continue to help if you need follow up information , all i ask is that you PLEASE take a second to rate my service so i may recieve my credit for assisting you. Thank you.
Customer: replied 1 year ago.
do you have a diagram of where factory trailer plug in would be? so i can check if i have it. i have a 2001 ford f150 xl 4x4 4.6L V8
Expert:  Lou P. replied 1 year ago.
If you follow the wiring from where you plugged in the trailer adapter , follow it down the frame toward the rear of the bed. If you have the connector it will be a round connector sticking out of the wiring harness just dangling there.
Expert:  Lou P. replied 1 year ago.
http://www.mediafire.com/view/6pkglkde5spx6qt
That is a link to how it will look. There were two options. Light duty or heavy duty towing but the connectors looked the same just different amount of pins.
Hope this information helps. Please take a moment to rate my service. And get that wiring harness from autozone and try it. If it doesn't work let me know and I can tell you how to splice into the wiring. Lou
Customer: replied 1 year ago.
I did find a factory trailer hookup zip tied to my frame it has a 7 pin and a 4 pin hookup. When I test the 4 pin same results no right turn or brake lights.