Trailer Lights...only running lights work properly.

[TomCat_Ford]

Hey guys,

I'm in the process of trying to sort out my trailer light issues. I would like to be able to pull our boat (18ft Four Winns) without having to keep borrowing a tow vehicle. The factory 4-pin plug that was on there was shot. So I picked up a new 4-pin plug today (one with LEDs in it to let me know if it's working at the pin) and spliced that onto the factory connector's wires.

All of that works fine, my Ohm meter ohms out on each of the wires. Also, my running lights work just fine. The problem is that I have no signal lights and I have no brake light (which seems odd being that the running lights work). Only the LED for the running lights comes on when the lights are on. It's not the LEDs, I have 0 volts on the signal and brake when the running lights are off.

Any ideas as to why these aren't working? The 15amp fuse inside the driver's door is good. I'm testing all of this without the trailer hooked up; the boat is stored at the campsite where we do our boating...I'm 100 miles away.

 

[TomCat_Ford]

Just pulled out my manuals, it told me to test the relay (2). When I test that with the Ohm meter, I get no responds when it's supposed to read 5ohms. It tells me to repair circuit 57 (bk), which is the trailer ground.

Does the trailer need to be hooked up?

 

[Ranger379]

Does the trailer need to be hooked up?

the trailer doesnt need to be hooked up for the trailer plug to work.

does yours have the tow package? the 4flat plug on the truck will lead up to a 4prong plug under the drivers side tail light. if so, maybe its bad, i would check power at that plug.

http://www.etrailer.com/Custom-Fit-Vehicle-Wiring/Ford/Explorer/1999/118241.html?vehicleid=19993130

if you DONT have the trailer tow package, follow the wires from the trailer plug and see where they go, 2nd gen explorer have the seperate amber rear turn signal, and a tail light converter is needed in order to run the stop/tail/turn style tail lights on the trailer.... anyway if you have one of those tail light converters, that may be your problem, mine didnt last long on my old 96 explorer. my trailer tail lights stayed on even when the trucks lights where off lol... the box was all melted haha.. that box would be behing your drivers taillight (remove tail light) heres a pic of the converter, its the big black box in the middle

http://www.etrailer.com/Custom-Fit-Vehicle-Wiring/Ford/Explorer/1999/118345.html?vehicleid=19993130


also, check the power distribution box under the hood, when i had trailer wiring problems i blew the big maxi 50amp fuse in there. might be worth checking that

 

[TomCat_Ford]

I have the tow package, the plug is there and the wiring harness to the 4-pin plug was an OEM Ford part (original, from what I could tell). There is no power at the connector. The only place I have power is the brown wire for the running lights.

I do get a pulsating negative reading (voltage reads 0, but the negative sign flashes on my volt meter) that blinks with the clicking of the hazard lights.

I shall check the big fuse now.

 

[Ranger379]

I have the tow package, the plug is there and the wiring harness to the 4-pin plug was an OEM Ford part (original, from what I could tell). There is no power at the connector.

I do get a pulsating negative reading (voltage reads 0, but the negative sign flashes on my volt meter) that blinks with the clicking of the hazard lights.

I shall check the big fuse now.

ok so you unplugged the 4flat harness at the round plug under the taillight and thats where your checking power?

im not very familiar with volt meters.... i just use a simple test light lol

 

[TomCat_Ford]

Yes, I unplugged it at the round plug behind the taillight (I can get to it from under the vehicle).

I went and checked the large fuses...all were good. So then I went through and checked all of the other fuses just for laughs...both 7.5 amp fuses for the blinkers/brakes were blown. I wish I would have noticed those sooner, but skipped right over them earlier. I now have blinkers/brakes, but...

The blinkers and brakes only work when the running lights are off. The test lights on my plug (that plug was worth the extra $1 it cost!) indicate everything works so long as the running lights are off. Any ideas as to why?

Oh, I normally would hear you on the volt meter, but my test light doesn't seem to be working, and I forgot to buy a new one when I was out earlier.

But I'm done playing with it for the night...time to spend some time with the Mrs. (who was growing ever-so agitated with me and my need to get this fixed) and watch some fireworks. Happy Independence day!

 

[Ranger379]

when talking about the blinkers/brakes, do you mean the blinkers/brake lights on the truck? or on the trailer plug?
did you check ALL the fuses? sounds like a short somewhere

 

[TomCat_Ford]

The Explorer lights all work just fine.

It's the trailer blinker/brake lights that work with the running lights off, but don't work with the running lights on.

I stumbled across a few web pages earlier today that talked about such an issue, but I'll play around with it more tomorrow.

 

[Ranger379]

The Explorer lights all work just fine.

It's the trailer blinker/brake lights that work with the running lights off, but don't work with the running lights on.

I stumbled across a few web pages earlier today that talked about such an issue, but I'll play around with it more tomorrow.

ok was getting confused wanted to make sure you where talking about the trailer plug... but i would say you have a short, maybe something not grounding, but id say short. i have never followed the factory harness, so i dont know where it goes, but i would follow that and see if you can trace those wires, good chance something maybe have rubbed on the frame, or got corroded, or it might even be the reason your blinker light and brake light fuse blew in the first place....

i had a similar problem on my 95 (hardly ever tows my trailer) the lights where all messed up, turn signals on truck came on when u hit brake pedal.... couldnt figure out why... then i opened my trailer plug - (rv-7) and it was full of mud. the water in the mud made enough connection to short the prongs...

good luck, let me know what you figure out tomorow

 

[TomCat_Ford]

I still haven't gotten a chance to check into this any further, and it's just too darn hot outside for me to even want to try at this point.

At any rate, I shall try to trace those wires, but it won't be fun. That connector goes up to a main wiring harness that is covered with the corrugated plastic/electrical tape. A few areas likely won't be accessible (easily).

 

[TomCat_Ford]

I finally figured the problem out. The filament on my passenger brake light was out, and there was some sort of issue with the bulb holder. I had a spare, so I plugged that in with a new bulb, and that fixed the brake light issue. For kicks and giggles, I plugged in my trailer wiring harness to see if everything worked...and everything now does, according to the LED indicators on my plug. It must have been the open brake light circuit causing my light issues when the running lights were on.

 

[thebrakeman]

I'm glad I just read this thread. My Dad has a '98 ('99?) F150, and has had a similar problem with certain lights only working under certain conditions. Can't remember the specifics, but this really sounds familiar. I'm gonna send a link to this thread to Dad.

Thanks!

 

[TomCat_Ford]

Not a problem, I figured I'd update it so that there was an actual cause in the thread...especially since it was so simple. I know how it is to read a thread and not find out if a solution was ever found!

 

[cstover070304]

I just went through this. Mine was the blown 40amp PAL cartridge fuse in the underhood fuse box.