Borrowed a buddys trailer that had wiring issues. I ended up blowing a mini fues & maxi fuse in my truck. 06 F350 CC
Replaced both fuses in the truck and had park lights on the truck but now dont get any lights on any trailers. All factory plugs 7pin & 4 pin.
I get turn signals and brake lights on the trailers but that is all. If the fuses are good were should I start looking for problems? or is there more fuses I may be missing.
I have metered all the fuses under the dash aswell as under hood all check out.
Were to go next ???

 

Have you checked fuse #38? This fuse feeds two relays in parallel for trailer back-up lights and marker lights. I would also check the relay for the marker lights which is located in the Power Distribution Junction Box under the hood. The relay is marked TRAILER MARKER LAMP RELAY on the schematic you will find at the link below.

https://www.fleet.ford.com/truckbbas...bb_pdf/166.pdf

 

Thanks for the info. I have replaced #38 fuse, & also a larger 20amp maxi fuse for the trailer. I cant open your link here at work so will check when I get home. Hope it is this relay and not some fried wires!!

 

Well I'm at a loss. Never was good with electrical. I have replaced #38 mini fuse & #115 maxi fuse. I pulled every fuse in the truck & checked them. I also pulled every relay & swapped them around to see if 1 was bad.
I could never get power to the trailer park lights. Everything else works. Now I guess it is down to metering the wire from the trailer plug all the way back to fuse panel & see if I find a bad spot?? I'm sure this will be a big pain to find all the connections under the truck!

 

ok here is my 2 cents on trailer light problems. 1. Bad ground. 2 bad ground. 3 bad ground. 4 bad ground. 5 some other problem. brake lights and turn signals have been known to backfeed? on them selves and create a "floating" ground.. any trailer issues I always check the actual white ground wire on both sides of the plugs. the ball is not a good enough ground. grind or sand a clean bare metal spot and make a GOOD connection on each end. to test leave ball unhooked and use ohm meter from tgruck to trailer. you want the wire to be the ground not the ball. next check the 3 hots, truck side first. then trailer side. next is light bulbs, are they the correct ones?
are they good? when all else fails, back to ground.

 

I'm not even looking at the trailer at this time. I have no power for park lights on the truck side plugs. That is why I will start to meter everything backwards & try to find all connection points.

 

Also pull off the 7 pin plug on the truck. Many have found corrosion inside it....Clean up this connection...I would start there then work towards the front. With DC circuits, if you don't have a good ground, it's the same as not having a hot wire. You HAVE to complete the circuit for it to work! This means, no (or bad) ground = no power.

 

If you had a good ground for your meter and had no power on the truck plug then you can eliminate a bad ground as the problem. When you were checking for the marker lights did you check any other circuits to confirm that the meter was properly grounded? Did you check to see if the relay was energized? Even if you have a good relay there could be a problem with the wiring to the coil. The relay coil is fed in parallel from the headlight circuit and the brake controller and also requires a ground for operation.

If the relay was energized and you didn't blow the fuse then you can eliminate a short circuit.

If the ground is good and you don't have a short then an open circuit is the culprit. I would start by checking the mechanical connections at the truck plug and then the relay. These will be the easiest to check. I'm not sure if there are additional connections under the truck or not.

 

Thanks Cowboy.
Yes the ground was good. I was able to meter back up lights, turn signals, but no power for the park lights.
I have a buddy that is good with wiring I will be going over the rest of the checks with him. I just dont know enough about elec. and dont want to wreck more than already is.

 

Alright Cowboy, I'm back for more help.
I have gone through every fuse & realy I can find. No luck finding a bad one.
When pulling the bad trailer I blew fuse #38 (trailer tow park lamps) aswell as #107 (trailer tow battery charge)
What # are the relays & where are they loacted? I have 2 realys right behind Driver side headlight. Then a bunch together Driver side firewall.
I have power to #38 and #115 fuses in the schematic you provide above. Now I just need to know I'm checkig the right relays. I used my meter and have power at all relay locations.
Just want to make sure I havnet missed any.

Plus I crawled under the truck and followed the trailer wiring back to front as best I could and cant find any connection points. So no bad connections yet.

Thanks for anymore help.

 

When you have a good fuse in #38 & #115 and the trailer is disconnected do you have power on the pins for marker lights & battery charge? If yes then the relays are operating properly, if no then there is either a problem with the relay, with the circuit which powers the relay coil, or with the circuit from the relay contact to the trailer connector.

If relays are your problem they will be located in the power distribution junction box under the hood.

If your relays are operating properly and your blowing fuses then this will be caused by a short circuit or an overloaded circuit. A short circuit could be anywhere the copper portion of the wire comes into contact with a metal surface. This could be where the insulation has been damaged or where a connection leaves some copper strands exposed. These can sometimes be difficult to find and will require a through examination of all of the wiring in question to find the problem. An overloaded circuit would simply mean that the circuit load requires a greater current than the circuit is rated for. This could be the problem if additional lights or loads have been added to the trailer. You will need to review what is is connected to the circuit and add up the current requirements. If it is greater than the fuse ratings then this is your culprit.

 

You might also check above the spare tire. I had a plug on mine there that I had to clean. I used electronic cleaner from autozone, I just dont remember if it was the F250 06 or the 04 I had.
I do remember that on the 04 that the running light wire on the 7 plug was dead and I never could find the problem. So I jumped off the license plate light wire and it worked fine with no problems. I dont know how big of trailer you use, but mine is a tandem 6.5X12 with brakes.
Good luck with yours.





__________________________________________________ ______________
06 F250 CC 4x4 6.0 with all opts
04 F250 CC 4x4 5.4 --- RIP

 

Thanks Lucky. Thats sounds like what I'm going to have to do. Run a jumper wire. I have metered every possible location swapped every relay and still no power to trailer lights. Then it will be a summer job when I can pull stuff apart & not break in the cold.

 

Well guys thanks for all the help. After looking at the wiring pics Cowboy put up I couldnt figure out where those realys were located. Well I now know that off of fuse #38 the 2 realys are NON-REPLACABLE!! they are soldered right onto the fuse panel circuit board.
How stupid of an idea is this, to have NON-REPLACABLE parts on a main circuit board, that is for Trailer wiring. There is always 1 thing or another going on trailers.
Now I need to see what a complete fuse panel is going to cost!! Or find a computor shop to see if they can replace the bad realys??

 

OK - so I read about relays and fuses to help resolve this problem. In the 2010 Ford Expedition, a main 25amp fuse will also cause the running lights to not work. It's fuse #28 in the front engine compartment. Hopefully this will help someone else find the trouble quicker than I did.