I recently towed my boat and when starting to backup the trailer the disc brakes stayed in the locked position. I also am not getting the backup lights on the trailer to work now although they had worked fine before.
I replaced fuses and 2 relays but still no luck. Consequently, I have to put the brake lockout clip in whenever I back up which is a real pain.
Is there something else in the system that I'm missing here that should be checked or replaced?

Thanks a bunch,
Bill

 

Depending on the controller, you may have an option to lock this function out on the controller.
As for the backup lites, there is a dedicated relay and it's fuse that may be a problem.

 

I'm a little confused: First of all, do you have surge brakes or electric brakes on the trailer? Second, if they're surge brakes, is the system equipped with a 5th wire for a dump valve for reversing? Third, if the answer to #2 is yes, then have you checked for power at the appropriate wire when in reverse? Fourth, if the answer to #3 is yes, is the valve on the trailer working properly?

Simple problem to track down.... honestly.

-Joe

 

Which 2 relays did you replace ?

There are 3 total that are for towning, the one that is for the reversing lamp is R301.

Which fuses did you replace ?

F105 is the electric brake control module

These are with the Factory tow kit, using the factory ( or aftermarket ) pig tail to the connector under the kick panel on the drivers side.

I have to ask one more stupid question that Joe did not post. When was the last time you towed with this truck and tailer and it worked correctly ?

The factory tow schematic :
https://www.f150online.com/galleries...028-149220.jpg

7 pin trailer plug pinouts
https://www.f150online.com/galleries...028-149221.jpg

I have the entire factory tow documentation that comes in the plastic bag in the glove box when the truck is delivered in pdf format if you want it.
Just drop me an email in my profile, and I'll send it off later.

 

Thanks for the information guys. I had purchased a repair kit from Ford and it did only have 2 relays in it which I replaced. After I checked around some more after my post I found that relay 203 wasn't part of the kit and when I replaced it things worked fine.

What I don't understand is that this was the first time I ever hooked up a trailer to the truck. It worked fine to begin with when backing at the launch ramp and back where I purchased the boat. However, after driving home for about an hour and then trying to back into my driveway it didn't work. Consequently, I had to put the surge brake lock out clip in to allow me to back up.

Is there some particular reason a relay would fail like that. Just seems odd to me but I'm an electrical novice for sure. Does a relay fail if there is a short? I thought the fuse would blow first but they were all fine.

Thanks for the posts!

Bill

 

I had the fuel pump relay give it up on my '01 at about 54K miles. It was really strange, I got home, parked the truck, went to start it ~4 to 6 hours later, and crank no start.

Some times they just take a powder, for what seems to be no reason.

Remember these relays are not solid state devices, it is a coil that pulls in the contacts and and make the circuit. Sometimes the coil gives up, other times the contacts that get pulled in, don't move anymore.
If you smell the relay close, you might smell the potting material, which might indicate that the coil gave up, and stopped working. It would kind of be that Transformer gone bad smell, or if you have ever smelled a TV that blew a transformer. It is a distict smell.
If you have the bad relay still, use a hack saw blade, and cut around the outside of the cover, and you can take it off, to see what happened inside.

 

When backing on level ground or down-hill at the ramp, the the brakes aren't doing anything, so not having the dump valve (or lock-out) in place doesn't really affect anything. However, when you go to bak it up-hill into your driveway, the brakes actuate, and then the harder you push, the tighter they lock. The relay likely wasn't working at first either, you just didn't realize it.

-Joe

 

Disc Brakes for trailers have solved all sorts of problems, but caused some new ones. For instance, with surge brakes, as soon as you slow down or back up and the coupler moves forward, you actuate the small master cylinder in there which actuates your brakes. Exactly the same thing happens for disc or dum brakes, except that discs are a ton more efficient. So they tend to lock up.

To solve this problem, they added a 5th wire which is connected to your reverse light circuit. When you put the truck in reverse, you energize this wire. When you energize this wire, you trigger a solenoid in the trailer brake circuit which literally shuts down the flow of brake fluid from the master cylinder to the calipers. So, you lock out the brakes.

When your reverse light circuit doesn't have any power, you cannot lock out the brakes and you can end up looking pretty silly. Once when this happend to me (delivering a customer's new boat), I simply rigged a jumper wire from the brown lead (parking lights) on the truck to the blue lead (trailer brake solenoid) and turned the parking lights on. Later on, I replaced the blown fuse.

 

Another way they can get around that with drums is they will install a free-backing drum brake setup (Dico used to have some good diagrams and animations). Even if the surge brakes were applied when backing, they were VERY ineffective, and didn't pose much resistance when backing. I had 'em on my boat trailer and never bothered to flip the lock-out switch in 8 years. I suppose if I was backing upt a LOOOONG STEEP hill, I might think about it, but in 99.9% of my use, it as completely unnecessary.

Do the electric lock-outs usually stop the flow, or just dump it back into the reservoir?

-Joe

-Joe

 

Joe,

All of the ones I've seen so far just stop the flow. Not a bad idea though on recirculating it.