I have a 1999 E-150 with a 7-pin trailer plug. I tow a Starcraft tent trailer. We were traveling and I began to notice that the running lights on the trailer looked dimmer. As we traveled they kept getting dimmer until almost out. Turn signals and brake lights were also dimmer. I used the hazards until we got home.

I used a test light and have good voltage at the van connector, but only for the battery charging pin. The pins for turn signals, brake lights, and running lights have voltage, but very low (I'm getting a meter today to see how low). For the running light pin, the test light would barely light.

I used a 12v battery and ran jump wires directly to the connector on the trailer and the lights burn bright, so I figure its the van. I checked the relays and fuses, and even swapped a few relays to test, but no change.

Is there a voltage regulator for the trailer harness? The rest of the van seems fine with bright lights.

Thanks.

 

I could suggest using the meter to measure the resistance between the ground side of the trailer lamp sockets, and the frame/battery ground of the truck. just as likely to be a bad ground somewhere.

 

I agree with BarryFS, this sounds like a ground problem. Do you have a "hard-wired" ground to the trailer frame, or are you using the hitch itself? Many times, relying on the hitch will cause problems due to rust and other resistance in the coupler.

I would try running a test wire from your vehicle frame (confirmed good ground) to the lamp sockets. If this works, you will need to either hard-wire a ground to your trailer frame from your tow vehicle, or replace your ground wire connection with a new one after cleaning the hole.

 

I would agree with checking the ground first and running a cable directly to the trailer.

Here is another thing to to think about. Your wires are too small to run both the van and trailer lamps. On most Ford trucks it is 16-18 gauge and vans have a fairly long wire run, couple that with the length of wire on the trailer and you are probably exceeding the wires capacity to deliver current or the headlamp switch.

What you might wish to do is run a (fused/relay!) 8-10 gauge power cable to the hitch and use a relay system for the trailer lamps. They sell kits for this or you can do it yourself. Usually they are called battery isolation kits or such.

 

An easy ground check is to use one side of a jumper cable. Attach one clamp to the trailer frame and the other to the truck frame.

 

I'll check the ground tonight.

 

I am having the same issue. Have turn and brake lights, but no running lights. About a year ago I had dim running lights and now they are out all together. Started checking things and I have 8 volts at the back of the truck for Turn, Running and 10 volts when the brakes are applied.

Thought it was a bad ground as 99% of the posts state, but I have dead gound (full continuity) from the plug to the frame there is 0 resistance telling me the ground is good.

So I started tracing up the truck to the various harnesses / connectors. All have 8 volts. Got to the engine compartment. I have pulled all the fuses in the power distribution box in the engine compartment that deal with the camper. Fuse #10 (that controls 14 and 22 for the lights and battery charge) has 12.5 volts. The other 5 or 6 fuses for the camper all have 8 volts. All the non camper fuses have 12.5 volts.

By unplugging all the fuses, I should have eliminated bad ground from the fuse box to the back of the car, according to the mechanics I have talked to and a Dana automotive engineer. Therefore since I am gettng 8 volts in the PDC for all the fuses, their presumption is that I have a bad hot wire from the power source to the PDC. It was maybe bumped during an alternator repair or something. Thus corroding or breaking some of the strands of the wire and giving resistance.

Can anyone here confirm they have run into this or that it truely is a bad ground even after all of this testing and eliminating?

 

Just to be sure I took off some of the grounds and regrounded them. No change.

More breaking details. I have 8 Volts on the Battery Charge Fuse at the front but do not have anything on that pin on the connector. Furthermore, with the negative battery cable disconnected, I still have 8 volts at the Fuse Box for all of the camper hookups. Convice me I am wrong, but this sounds really bad. I am getting negative voltage on some of the other fuses in that box. Guessing at this point that I have a grounded wire somewhere in the camper hookups, likely the battery charge cable since that is not working at the plug. Help...

 

Odd though that all the blinkers and brakes work just fine (on low voltage) with the wires frayed (?) and the only thing that is not working is the running lights (and I guess the battery charger).

 

If you are indeed getting 8 volts or so at the fuse box (PDC) then yes you have a problem with incoming power. At the fuse box with nothing hooked up, all the hot fuses should measure the same voltage. Not 12.5 on most and 8 or so on the camper. Here is my guess. The main wire feeding the PDC for the trailer circuits got maxed out at some point, caused the wire to get hot due to the amperage and burnt up some connector(s). I would look for a heavier wire to feed that portion of the PDC if possible. In the end you should be reading the same voltage on all the fuses in the box with no trailer hooked up. Once the trailer is hooked up, they should be within 1 volt. Battery charge may be outside of the range if the battery is really low.

 

I need to find which wire fried, you are right. My current (pun) problem is that I am getting voltage in the system with the negative battery cable DISCONNECTED. When I jump from the tail lights to the frame I get 8 volts, when I jump from the Battery Negative (disconnected) to the tail lights fuse I get 20 volts. Yes 20 volts, I had to change the setting on my VOM to get the reading. How in the heck do you get 20 volts going through a 12 volt battery. Is there the slightest possibility that the factory installed an extra battery or something in this system, I have no clue how this can be happening. Also, I cannot figure out how to open the power distribution box. It seems there are simple latches on the side, but I cannot seem to raise the cover to get to the under wiring.

 

More info. HOLY CRAP!! I just discovered I have a second battery in the van that is mounted on the frame under the back passenger door. Never heard of this. Disconnected it and now my fuses are not registering 8 volts in the PDC.

 

Does that mean they are normal 12V or 0 volt? If they went to twelve it is probably the extra battery is bad, shorted plates causing the drop. Just my guess though.

 

Turns out that I have the optional, and very infrequently implemented, auxiliary battery that I cannot even find listed on the Ford website. There are exactly two paragraphs on it in the manual (basically don't forget to disconnect it, IF you have it, before working on the car.) The net result is that there are two electrical systems in the car, one for the main vehicle functions, and one for the trailer vehicle electric. Like a boat has two batteries one for the engine and one for accessories. This way the trailer's systems cannot kill the van's functions with battery drain. This seems to be available on the E-150 Chateau Package.

I had to work with Sears to get them to even work on the car, and in the end the Diehard Crew came through. Three hours later, both car batteries were changed and the corroded heads for the Aux Battery were cleaned up. Once everything was reconnected, I had 12 volts at the back of the car and in the PDC box.

The 8 volts were coming from the nearly dead battery, where one of the cells was fried and any load causes cessation of function. When I pulled the ground wire from the aux battery, the car was fully disconnected and I finally had disconnected circuits. When I got 20 volts, I had inadvertently probed the two batteries in series.

For future reference, the battery is located under the rear passenger door in a rusty box that says "Don't touch unless you are certified".

 

Cool, sounds like you got it covered then, good deal and happy motoring.