I have a 2006 F150 xl with tow package. Just got a trailer with a 7 pin connector. Hooked it up one day and while raining it shorted the trailer harness on the truck. blew fuse 36, 42, and 105 and smelled electronic ozone from the area of the driver side fender well. About the same time the trailer brakes started to alternate between on and off and the brake controller started to indicate a short. I pulled the trailer connector but the damage was already done.

I replaced the fuses and did not see anything obvious from the fender well area. Let the trailer connector dry out and water proofed it.

Left and right turn signals work on the trailer, tail/running lights are very dim and the brake lights are on all the time.

the brake controller does not see a connection to the electric brakes on the trailer and brakes do not activate.

7-way Trailer connector from etrailer

Using a multimeter to get voltage readings I get the following

14v on black
14v on brown
14v on blue
12v on yellow when activated
12v on green when activated

seems to me like I have a relay or harness short someplace on the brake circuit which is bleeding through to the tail/running lights or visa-versa

any ideas on where to start?

 

Is this on the trailer only or the truck as well ?
Do the truck's lamps work correctly
- Pay attention to the brightness of the stop / turn element vs the parking lamp element.

You have + VDC on the blue wire at all times ?
- This is the output of the brake controller, and should only have power when the brakes are on.

Is your black wire a black w/ pink stripe wire ?
- This is the reverse lamps wire, and should only have + VDC when the truck is in reverse.

Do you have a solid ground on the white wire ?

Do you have + VDC on the orange wire only when the key is in the run position ?

I would take a SWAG that there are wires melted in the 7 pin trailer tow adapter for how strange some of the readings are.

Take the 7 pin adapter apart from the back, and check the wires going into the socket for signs of damage.

It is easy enough to replace the harness, the connector is up along the frame rail under the spare tire if you need to replace it.

 

The readings are from the vehicle with no trailer attached and no brake pedal depressed.

yes brake lights are brighter than running lights when the brake controller is activated manually. The trailer exhibited continuous brake lights and blinking turn signals, dim running lights. truck lights did not appear affected

YES, even when the truck is turned off I get 12 v dc

NO

the trailer did not have ground wire back thru the pigtail. all items were grounded on the frame which then connected to the vehicle thru the ball hitch.

I have a brown wire not an orange. i only have 12v when the running lights are on... mV when not

 

You need to keep the testing to the truck only at the moment.

You have the readings being taken at the factory trailer tow adapter without the trailer attached and the brake off, but when I ask about the battery charge circuit, you mention the trailer..
- I do not know how the trailer is wired or if the manufacture ( or other ) followed a standard wiring color code.

The truck has a white wire for ground, If there is an issue with this, the trailer will not have a ground.

- Check the truck's 7 pin trailer tow adapter ( without the trailer plugged in ) for a good ground on the white wire.



Need to take the trailer tow adapter apart from the back to check the wiring for signs of damage.

I still have the SWAG that there is damage inside the trailer tow adapter, but without confirm it is just that, a Guess.

 

All readings are being taken with no trailer and on truck only with no brake

ok based on your diagram my black wire is your orange wire.

0 V dc with key turned off (actually 388 mV but that is not much)

also with the brake controller plugged in and NOT activated with truck turned off I get 12 V dc on the DB wire

I currently have another controller on order to replace it. If that's not it then I have a spare.

ground wire zeroes out when tested

I inspected the trailer harness at the receptacle and there were no tell tail signs of melted wiring.

The 12 V dc on the brake controller has me thinking I blew that box up and it now has a open short in it. Will know more when I get the replacement

 

Quick update. I purchased a 7 pin to 4 pin adapter/tester and set of magnetic lights. It looks like my harness on the truck survived. I will now investigate the trailer. I do believe the pig tail may be damaged and needs to be replaced.