My truck: 2004 F250 SD GAS With factory towing package.

Just recently bought a travel trailer. When i plugged my truck in the running lights on the trailer worked, but no blinkers, brake lights or brakes worked. I went out and bought a new bargman trailer plug and rewired it accordingly on the trailer. But before doing so I took my meter and tested the hook up on the truck to verify all the functions were working.

When i hooked the new plug into the trailer harness I still only had running lights. No other functions. I took my meter out and tested the voltage for each function. My blinkers, brakes had less the a volt for power while fluctuating.

I decided to test my trailer by take a hot lead from the trailer battery and jumping it on each function. Ie. Right turn, left turn, running lights, brakes. And all the lights worked as they should. I am sure now that the trailer itself is not the issue. So my question is where should I start looking on my truck. What would cause the voltage to drop when there is demand? I know my battery is bad as if I leave my lights on my truck for more then 3 minutes or so while the truck is not running my truck loses power and I have to jump it.

But shouldn't my alternator keep up with the demand of the truck plus the lights?

Suggestions would help...and yes I know grounds first!


Thanks
-Nick

 

I had an issue last week with my lights for my trailer. I had a fuse blown in the fuse block under the hood. Something so simple I didn't think of it, because it worked fine a couple of weeks earlier.

Also having a bad battery might play into the problam. The trailer might be putting to big of a load on the alternator. When the trailer is plugged in you should also be charging the trailer batteries, which is a load.

 

Behind your truck bumper plug, there should be another connector up around your spare tire, I've had problems at that connector before on my '04, take it apart and clean it. Chances are you're getting a bad connection there. Good Luck.

I also had problems with the factory 4 wire flat connector (which I never use), if yours still has it it may be all corroded under the cap cover. After my 3rd (long stories) replacement plug on my truck I finally just installed a 7 wire connector through the bumper and got an adapter for the 4 flat.

 

Trailer load on alternator is unlikely to cause this problem. If amp draw were that high, you would also see it in truck.

I am not sure I am following your post. Loss of function on multiple systems is almost always a grounding issue. if you are dropping voltage, it can also be a connection issue. The problem with using voltage as a test measure in this situation is you really need to know amp draw. Going to another power source does not clarify the seven pin cord to the seven pin receptacle on your truck.

The seven pin in Ford trucks is an ongoing problem given the location of the ground pin in the receptacle.

Steve

 

I do a lot of trailer wiring repairs. Almost always I find dirt built up in the connections reducing the max voltage. It is not just grounds but all the connections. I pull the rear plug, clean out all the dust and dirt, grease the slide fittings and reclamp the wires in the plug. Some plugs have enough room for crimp fittings to pinch between the screw and the clamp. I like this and find it lasts longer.

If the plug on the bumper is good and I still have issues I then pull apart all the connections to the harness. I find some real interesting crimps, solders and wire wraps that should never have worked. Factory plugs seldom seem too be the problem.

To make the testing easier I mad a quick trailer lite tester that I plug in and set on the ground facing the drivers door. I can test all in a few seconds.

Good luck. It is not just the grounds it is all the wire connections with a trailer. Old trailer lites also corrode int he sockets. Cleaning out the sockets gives a brighter lite.

 

He established trailer lights with his initial testing.

Steve

 

Steve??? So as a master tech you are saying a bad battery and the need to replace the trailer plug would keep you from testing what I suggested??

If the plug on the trailer was bad the light sockets may also be bad. The lights will shine but not as bright as they could and should. If the truck rear lights work but the trailer plug does not then as I suggested look at the connections at the rear of the truck and clean them well. Using grease on all plug ends helps with old wiring. If the truck wiring is bad it is a slow process tracing the wires back from the socket to the power source. On a 2004 Ford the wires run along the frame rail to the cab. Easy enough to find a short. After that trouble shooting is hard. It sounds like the OP has good tail lighting and the problem is only with the trailer harness connecting to the main harness.

My suggestion is first a new battery then checking the connections. No one should go on a camping trip with a battery that dies within a few minutes when lights are left on.

Steve if you cannot be productive with postings then at least be clear with why you would bash anothers post. Supporter or not, expert or not help or keep comment to self.

 

I don't think Steve was bashing your post. I think he was just stating what I have already said here. The trailer wiring is not the issue. I can get all the functions. (Brake lights, running lights, and turns/hazards) to light on the trailer when attaching them to direct power. The only time they do not function is when plugged into the truck.

The truck still works alone by itself. In fact using my volt meter I can watch the voltage fluctuate as it should with blinkers, hazards and brake lights. But.... When I take a new bargman plug (not wired to the trailer) and plug it into the truck and put a test light on the functions it does not light. And for a fact the voltage then drops to less then a volt while still fluctuating. I am almost certain it is a bad ground or something is wired incorrectly at the truck.

Thank you everyone for the suggestions... keep them coming and as I figure this out I will keep this updated.

Thanks,
-Nick

 

Maybe one of the blades in the 7 pin socket on the truck is not making a good connection to the plug (maybe the ground). You've tested every pin in the socket (truck side) and it functions as it should. When you plug in the pigtail (not attached to a trailer) and tested the bare ends of the wires, you get a very low voltage? Right?

 

Try this:
Take a jumper cable from the rear bumper to somewhere on the trailer frame. Test your lights. Mine gives me weird faults so I made a short jumper to double up the grounds. Mine now works as advertised. The older they get the worse the grounds get.
My $0.02 worth.

 

I can test the 7 pin socket truck side and get good voltage when there is no draw. But when I put draw on it the voltage drops. For example I used my multimeter to test the voltage. My meter does not draw hardly anything to test as it runs off its own power source. But when I put a test light on the socket to test the voltage drops according to my test meter and the lights do not function.

Same if I test it from the trailer side. But when I test the trailer with battery power to the positive leads then lights function.

 

Hoping for the best here. Did you replace the plug on the trailer or the truck? If on the truck and the wires are still not giving juice, pull the plug and clean re-splice the wires into the socket. Better yet is put a new plug receptacle in. The big white wire is the ground and it does get corroded. Testing from a known good ground source to the hot leads is the best test method. We know the trailer is good for you but the truck ends can be bad in several locations. Since the existing lights work on the truck I would suggest either the trailer outlet on the bumper or the tee fitting tying in to the main harness.

 

i had a similar issue but when instsalling my brake controller it just says open circuit even when the trailer is plugged in idk what to do

 

Is there a relay for the socket? I recalled reading a thread saying that Ford supplies the relay for the socket in the glove box and you have to insert it to get the socket to work. If so, maybe the relays are weak and need to be replaced? Not sure where it's located. How about your flasher behind the dash?

Sorry, not sure what the issue is, but maybe I can give you suggestions.

 

Well... I fixed it. Ha ha. I feel really dumb here. I checked the signal fuses for the truck and since the plug socket had voltage I assumed it to be a ground issue. Never thought to check in the fuse box for separate fuses. Sure enough my brakes,turns fuse was blown for the trailer plug.

ha ha.... One of those "good job dumbie" moments.