[Sg29651]

So I'm trying to figure out why my trailer 12-volt is not working. I checked in the fuse box and apparently it is one of the relays that are in between the brake master cylinder and the actual fuse box. I installed a 30 amp fuse in place and now I'm getting power to the center pin which is supposed to be the backup lights. Does anybody have a wiring diagram for the12volt power system for trailer?

 

[bobofthenorth]

I'm not 100% sure exactly what your question is but this is the Bargman pinout. I believe Ford uses the centre pin - which is officially an auxiliary circuit - for backup lights. That may or may not match your trailer wiring. I've personally never seen a trailer with backup lights wired but there's plenty in this world that I haven't seen. The first rule of trailer wiring is that its ALWAYS the ground. You need a good solid frame ground on the truck side and the same on the trailer side. I have been fixing trailer wiring since I was 14 years old - my first summer job was at Holiday Wheels in Regina. There absolutely are trailer wiring problems that are not ground related but they are so rare as to be memorable.

To troubleshoot trailer wiring start with a plain old test light - your VOM is useless for this purpose. Test each of the pins on the truck side. Use the plug ground when testing the truck side. Then use a power supply and test every pin on the trailer side again using the trailer plug ground. When you've done that you'll know what is wrong.

 

[Sg29651]

I'm not 100% sure exactly what your question is but this is the Bargman pinout. I believe Ford uses the centre pin - which is officially an auxiliary circuit - for backup lights. That may or may not match your trailer wiring. I've personally never seen a trailer with backup lights wired but there's plenty in this world that I haven't seen. The first rule of trailer wiring is that its ALWAYS the ground. You need a good solid frame ground on the truck side and the same on the trailer side. I have been fixing trailer wiring since I was 14 years old - my first summer job was at Holiday Wheels in Regina. There absolutely are trailer wiring problems that are not ground related but they are so rare as to be memorable.

To troubleshoot trailer wiring start with a plain old test light - your VOM is useless for this purpose. Test each of the pins on the truck side. Use the plug ground when testing the truck side. Then use a power supply and test every pin on the trailer side again using the trailer plug ground. When you've done that you'll know what is wrong.

View attachment 158768

My question is oh, I'm trying to get the 12 volt charging to work to the trailer. There are two relays in a separate box next to the fuse panel that I believe is for the backup lights and also the 12 volt system. I installed a 30 amp relay in there and now all of a sudden I'm getting power to the middle pin connector But still not the 12 volt charging. I'm looking for a diagram to see where I need to trace the wires. Thanks every single light in the trailer it works just fine.

 

[klhansen]

My truck came with the relays and a maxi-fuse in the glovebox for the trailer towing setup. Also had a brake controller pigtail.
Anyway, if you haven't installed the maxi-fuse for the trailer battery charge circuit, it won't work. I believe the circuit is there to pull the battery charge relay in when the key is on, but without the fuse, it's not going to send power to the trailer connector.
Should be fuse #16, a 30A maxi-fuse per the wiring diagram for a pickup (you didn't say what you're driving).

 

[Sg29651]

My truck came with the relays and a maxi-fuse in the glovebox for the trailer towing setup. Also had a brake controller pigtail.
Anyway, if you haven't installed the maxi-fuse for the trailer battery charge circuit, it won't work. I believe the circuit is there to pull the battery charge relay in when the key is on, but without the fuse, it's not going to send power to the trailer connector.
Should be fuse #16, a 30A maxi-fuse per the wiring diagram for a pickup (you didn't say what you're driving).

7.3 powerstroke, I do have the fuse in slot #16

 

[klhansen]

I would start at the fuse, check that to be sure it's good, then probe the output wiring at the relay. Like I said, the relay should pull in when you turn the key to on, and the backup relay should only pull in when you're in reverse (also with key on).
Is the wiring at the trailer connector original? Or has someone butchered it up. They may have swapped the wires around. Give me a few minutes and I'll look up the wire colors for you, although I think the trailer battery charge wire should be orange.

[on edit] The wire coming off fuse #16 is black/yellow and out of the relay is orange to the trailer connector. You should also check fuse #24 (10A - hot in run) to be sure it's good. That's the circuit that activates the battery charge relay.
Trailer running lights - Brown/white
Reverse - Black/light green
Trailer brakes - Dark Blue
Left turn - yellow
Right turn - Dark green
Trailer ground - White