Reverse lockout - blowing fuse when backing the trailer

[woolznaz]

After 3 and a half of summers of no problems backing my trailer, I have an issue that just started. I have surge disk brakes and the trailer is wired so that when I put my truck in reverse it shuts off the actuator on the trailer brakes. All of a sudden, it is blowing a fuse on the truck. The truck is a 2006 F250 and it has a dedicated fuse for what the manual calls "trailer reverse lights". It's a 10 amp fuse and has never blown until the past two weekends when it blew each time.

The trailer wiring has the 5 wire flat plug. I have the adapter that goes from that 5 wire flat to the 7-pin round on the truck. Any thoughts on what has changed? My driveway starts off up hill a little when I am backing my boat back in and it blows the fuse there. I replaced the fuse once and backed it in fine. I was hoping it was just a bad fuse and since the new fuse allowed me to back right in, it seemed possible that my troubles were over. However, I knew the fuse may have just been doing its job and perhaps the new fuse would blow again. It did blow again the following week when backing into the driveway so I need to do some trouble shooting.

I don't know much about 12V wiring, but I do have an old analog multimeter I can use for troubleshooting. I assume it could be a bad ground or something on the trailer side of things.

Any thoughts or suggestions of how I troubleshoot this would be appreciated. BTW, I do have the manual "lockout key" I can put in to manually lock out the brakes. It works OK, but it does still allow the actuator to compress enough that the brakes do engage a little. I really prefer to get the electric lockout working again.

Thanks for any hints/tips.

[HandymanHerb]

You have a solenoid shorting out when you go in reverse, use an ohms meter to check to the solenoid for a short

[fiddlebick]

I agree that the solenoid is the first place to look. My system is brand new...I am now thinking it would be best for me to purchase a replacement solenoid to keep in my kit for the eventual failure. My brakes will lockup on when I backup on flat terrain without the trailer lights plugged in. If I were caught out with a bad solenoid that would be a major problem.

[woolznaz]

Thanks for the replies, guys. I assume we are talking about a solenoid located in the tongue of the trailer that locks out the brake actuator when the tow vehicle goes into reverse. Is that correct?

By a short in the solenoid, am I looking for chaffed wires or something like that around the solenoid, or is it likely just a faulty solenoid itself? Based on fiddlebick's comments, it sounds like this is a part that commonly fails.

Herb, if I pick up an ohm meter and test the solenoid, do you have a tip or two on what I am looking for? Assuming it is shorting out, what will the ohm meter read vs how would it read if there is no problem? Any tips will be appreciated, although I guess an ohm meter will come with some directions/tips on what to look for.

[stickman]

Pretty good troubleshooting guide here:

https://www.boatmateparts.com/manuals/m ... 073137.pdf

[HandymanHerb]

The only thing the reverse power runs to would be the solenoid.

A meter when placed in ohm position and you touch the leads together that is showing a short, not touching shows an open.

So if when you check the leads of the solenoid if they go the same way as touching the leads together the solenoid is shorted out, to check to see if it is shorting to the trailer, put one lead on the trailer and then touch the wires one at a time

[woolznaz]

Thanks again, guys. Good info. Stickman, that is a great write up. Thanks for taking time to post that.

[cwag911]

Make sure there's no power on when using the ohm meter. It'll fry the meter.

[woolznaz]

Update: Just thought I would follow up to let you guys know what the problem was. So often we start posts on here to look for help, and a bunch of people chime in with good suggestions. Then the OP never comes back to say exactly what was found. That's the key.... the most important step in a forum to help others learn from problems we all experience. I'll get off my soap box, but I wanted get that out there.... please follow up on your posts when you solve your problem so we can all learn.

Anyway, in my case, I realized I had used a different adapter than I usually use. My boat trailer has the flat 5-pin connector and my tow vehicle has the round 7-pin connector. Therefore, I have an adapter in between. As it turns out, I have 2 adapters. One of them has an issue on the blue wire (apparently) and it was causing my fuse to blow. I realized it was a different adapter (although it should be identical) so I decided on a long shot to use my other one, hoping it was a problem with the other adapter. Everything worked as it used to with my original adapter. So, in my case, it was a simple, simple fix. Not even a fix, really, but just switched to my other adapter. The funny thing is that a couple of weeks ago I pulled another boat (not my South Bay) 1400 miles using the "bad" adapter with no problems, but I don't recall if I ever tried backing up an incline with it on that trip. That boat/trailer is now sold, so I guess I'll never know if it is really a bad adapter or just some odd incompatibility between that adapter and my trailer.

I've only towed the South Bay a couple of times since, so I guess it is too early to say this fixed it for sure, but so far no problems. Thanks again for all of the help, guys. I appreciate the advice. If it happens again with the "good" adapter, then I guess I'll be doing more troubleshooting and using the great advice that was offered up.

[Silver Eagle]

When I had my bow rider and I had this problem I was told that the easiest cure was to just get out of the truck and disconnect the wires until I was ready to go forward. The other was is to get a manual switch. It fits on the brake line, No wires. That's in case you forget to hook up the wires.

[woolznaz]

Silver Eagle, I think we must have had different issues. My trailer has surge brakes, so backing up a hill will apply the brakes whether you have it plugged in or not. The brakes are NOT applied electrically. The "locking out" or prevention of the brakes being applied is what is controlled electrically. That solution would have had no effect on my issue at all.

There is a physical lockout plug one can put in place if the electric lockout is not working. However, you do not want to leave that in as it will keep your brakes from working going forward, too, so don't forget to take that lockout plug back out if you use it.

[kryptonite]

If you look at those adapters, they usually can be taken apart. They have 4 tiny screws in them. Sometimes there are a couple wires that can be switched to different poles. Not sure if this could have been your problem, but maybe the backup wire was hooked to the wrong pole or had a loose wire that was touching the ground inside the adapter.

I had a 6 pole round to 7 pole rv one time I hooked up to someone else's trailer and the electric brakes activated as soon as I plugged in to the truck. Well with the 6 pole round, there are 2 different wiring schemes. I noticed the adapter came apart and found that you could switch two wires inside - problem fixed. (The brakes were going to the 12+.)