Trailer won't back up

[Tom Edwards]

All vehicles in the last 25 years are that way until some introduced a module that protects the trailer wiring.

Never heard of it, never been in any position to hear about it, and I'm sure most GM owners also never heard of it, probably only those that have had a problem have heard of it. Let alone owners of other brands. But my advice is still accurate for all brands regardless of any equipment of that sort, and regardless of the age of the vehicle. Check for power in the middle and that'll tell you if it's the trailer or tow vehicle, then go from there.

[Tom Edwards]

All vehicles in the last 25 years are that way until some introduced a module that protects the trailer wiring.

Allow me to ask how you learned about that. thanks

[1BADAIR]

The truck uses the Body controller to power the truck reverse lights . The trailer has its own fuse. #16

[tdt91]

It doesn't really matter how anyone knows about something. What really matters is that people shouldn't spout off with stuff that they don't know about, especially when given the chance to step back and do some research. I wonder if Tom works for NBC, MSNBC, or CNN because it's common practice there.

[CatFan]

Allow me to ask how you learned about that. thanks

Maintaining many trucks for many years.

[Tom Edwards]

Maintaining many trucks for many years.

Thanks. I'm not a professional mechanic but have taken college courses many years ago, way before 25 years ago. That's how we learn, ask, and being exposed to new info/systems like this thread/post/questions and answering. Thank you.

[bassmasher]

Have a 2015 gmc and 2021 Phoenix 920 elite. The reverse lights on the truck work but not on the trailer and the brakes lock up in reverse. Is that a fuse on my truck and if so does anyone know which one? Or is it something in the trailer wiring?

1st question I have is did the reverse lights work prior on the trailer and did it back up with no problem before. If this issue just occurred check all of the grounds starting with the plug on the truck. Be sure the reverse prong on the trucks plug is getting power and then work your way back.

[BarryFL]

Other makes do it the better way, simpler, and so easier to solve and fix. :-)

Ford and Honda both have 2 fuse boxes and trailer specific fuses. What do you drive?

[Bartman]

Fuse 16 under the hood should be your first check. If blown, carefully examine the blue wire going the the solenoid for insulation damage.

This first

[Lkmbjb502]

Same thing happened to me. Got home with my new boat and couldn't back into my driveway. Used the lockout key on the trailer(and ordered one of the magnetic versions as a spare).

I never had backup lights on any of my trailers (or car trailer s either) so I didn't even know there was a separate fuse for backup lights on the trailer. On my 2019 F250 (or 2016-20 F250) it's fuse 84 under hood box, Micro2 fuse.

Told my dealer the about it and he said since I was using a flat-to-7 pin adapter on my old trailer, it can sometimes blow the trailer backup light fuse when combined with a trailer that doesn't have backup lights, like my old boat.

Not sure how it blew but swapped it for a new one and fixed the issue. Easy fix if that's your issue.

Good luck

-Jonathan

[Beandip]

My new truck which is a 2021 Ram has a parksense option you can turn on and off. If on it looks up the brakes when it detects something behind or in front of you and your trying to move. I thought my r brakes we're engaging but it was the truck locking up. Once I turned the parking sensor off, I've never had a problem since.

[steve1206]

These are good for an on-the-fly emergency...

https://www.amazon.com/Extreme-Max-3...026351614&th=1

[marshall256]

Have a 2015 gmc and 2021 Phoenix 920 elite. The reverse lights on the truck work but not on the trailer and the brakes lock up in reverse. Is that a fuse on my truck and if so does anyone know which one? Or is it something in the trailer wiring?

Sounds like no power to the reverse solenoid on the trailer at first glance. Dig out you truck's owner's manual and locate the fuse for the Trailer Harness Back-Up Lights. On my old Chevrolet Avalanche this fuse was under the hood with the other trailer harness fuses. As discussed in this thread, trailer fuses are on a separate harness vs. the vehicle lights - this change probably happened around the turn of the century or earlier. If no blown fuse, then you are going to need to check your ground wire on your harness going from the truck to the trailer. Although, if you have a loose ground...you could have other symptoms besides no back-up lights or power to reverse solenoid. Ground not the issue...then you might have a faulty reverse solenoid. It happens, but not as frequent as they used to and with your boat being new...I'd save this for last on my list of troubleshooting.

Last, all of this is assuming that everything was working right for you at one time and this isn't your maiden voyage. If this is your maiden voyage, then scrap everything above and start with your adapter that goes from your trailer 5 pin plug to your truck's Round plug...you might have the wrong adapter for your truck.

[GBhoss]

There are a couple things I would suggest trying.

1) Get a friend to come over with their truck and see if the backup lights work and the brakes are unlocked while backing up. This will take out of play the trailer wiring making the truck plug the issue.
2) If that works it is now the truck's plug that is bad or if you are using a converter (7-round to 5-flat) that could also be the issue. There is a tester sold in almost all auto parts store that you plug into your 7-round plug on the truck. Buy it. This will determine what is actually bad on the plug. You were unclear as to if the rest of the trailer lights were working.

I drive an F250 and had your exact issue. Backup issue only. There was a fuse blown and I found it in the fuse box under the hood (driver's side near the firewall). Replaced and it worked. 300 miles later I had the same issue. I ran a new blue wire (for the brakes) and have not had the issue since.