I'm new here so if I'm posting in the wrong area please let me know where to. I'm used to it. I just bought an 05 f-250 diesel. Everything seemed to work like it should until I hooked up to one of my trailers. No trailer lights at all. Nothing at the connector pins so I checked the fuses under the hood and under the dash. All are good. Used a test light on the wires going in to the back of the trailer plug and none have any power. At some point in the search I realized the trailer brake controller indicator light doesn't come on either, which I'm sure is related but didn't notice at purchase. Contacted previous owner. Claims he pulled trailers all the time and had no problems and no ideas. Is there one electrical component that would cut power to all trailer light and brake controller functions or am I looking at several problems?

 

should be several.. brake controller only does the brakes..

check fused again and if relays ..check them also.

check the rear side (wire side) of the 7 pin.. not just at the pins.

 

Like Chuck said. If you have no power to the seven pin on your trunk it is fuses or relays unless there is a wiring problem, which is less likely. Follow the wires back from the seven pin on the back of the truck to where they are connected, usually with a plug unless someone has jury rigged it and see if there is power there.

Just checking but have to ask since you have no power on any pin, did you have a good ground for your test light. A poor ground will mean no test light, but also could be the cause of nothing anywhere on the trailer and that is a really common problem. Especially since the previous owner said all was good to go.

Steve

 

I think some where around the frame near the spare tire is the connections for the trailer 7 pin plug to make it to the receiver.


I'd check there for power and I would also be tempted to pull the 7 pin connector apart and check the wiring at the back side of that for power.


Also you could check the connections at the back side of the TBC for power too.


It should allow you to press the slider and then see a fault prompt on the TBC of no trailer connected I believe.

 

I hoped someone would tell me there was one simple thing to solve this. So much for that. Before I posted here I checked all the fuses twice and pulled the wires out of the loom behind the factory plug going to the 7 pin and used my test light there. Still nothing. Good idea on test light ground could be an issue so I will check it first on truck tail lights since they work. Someone posted that you could buy a tester that plugs in to the 7 pin but my local pats store did not have one. I'm going to order one also a good idea thank you. Anyway I used a link shared on this site to look up fuse and relay legend for my truck since I don't have owners manual. There are so many fuses and relays related to trailer towing that it seems unlikely all of them have failed, especially since I did not find ANY blown fuses. Relays coul be the problem. Should I buy a couple new relays and try replacing those one at a time? I'm working out of town now and didn't bring my multimeter so I can't check that way. Does anyone know if there is a single plug for the trailer harness that plugs into the back of the fuse panel that may be the problem and if so which fuse panel and any way to identify it? I really appreciate everyone taking time to read and respond thank you for your help.

 

working from memory (bad idea)

power for tail lights/running lights.

power for brake lights/turn signals.

power for brakes

power to charge trailer battery

Ground. do not rely on hitch/ball ground...

test trailer to another truck.. just because. do not ask.

I have a 7 pin tester.. Very handy. got mine from etrailer dot com.

 

I could have several relays giving problems although it seems unlikely. If i don't find a ground problem first I will probably just replace them to eliminate that possibility. As for your suggestion to hook trailer to another truck, I asked my son to come over and hook his truck to it that day and trailer lights all worked fine. That's not it but I'm beginning to think you may be on it with the ground fault. It would be odd that my test light and the 7 pin would not ground at the same time. I'm going out now to check the ground theory and I'll let ya know what I find. Thanks

 

Go ahead and laugh, I can't hear you. What is the TBC

 

tbc= trailer brake controller

 

Damit, I knew that was gonna be obvious I just couldn't make my old brain work it out.
Anyway, the brake controller is not working. It's a very inexpensive model by DrawTite and I plan on replacing it with higher end unit as soon as I have time. Just checked and have power at unit and power out when I activate slider but indicator light on front doesn't work which led me to think unit was not working. Don't ASSume.

 

OK more encouraging news. I'm thinking y'all are gonna help me get thru this now. I tested my test light and it was not grounding. More good advice! Now it shows I have brake and turn lights but still no marker lights as well as no power to trailer brake pin and the trailer tow battery charge pin. I'm going to check those specific fuses for a 3rd time and then I'll have to wait till after work to get relays unless anyone has more ideas

 

EVERYTHING WORKS!!! Y'all are great. After using the fuse box legend that I got from a link on this site I found that the fuse for the marker lights and the one for the trailer battery charge were both missing. I tested all the fuses that were in the box but did not consider that some might be missing. Put in new fuses and, problem solved. I think the previous owner lied when he told me he had no trailer light problems. Anyway can't thank all of you enough for your help. You guys are awesome!!! What a great site.

 

Great outcome! And now you know more about your setup as well.


I used to have a prodigy p3 in mine old truck. it worked very good.

 

OP, thanks for the report Back..


YES x2 on the Prodigy P3.. I have one on the shelf.. from past truck.. to good to let go.

 

As the saying goes "it's always the ground" and sometimes a lot of other things too!

Steve