2008f350 trailer wiring fault. About to lose it here.

[Hampton_Bay]

We bought a 2008 f350 about a month ago. Engine was brand new, so now that we have a few miles on it we hooked up the trailer to check things out. This is where the fun began.

One brake stayed locked up. We ended up just removing that brake entirely because nothing else worked. Figured we would handle that later.

That’s when the “wiring fault on trailer” started. It didn’t do that when the brake was locking up. Sometimes it says wiring fault, sometimes it says trailer disconnected. The lights all work. When you hit the brakes, the red light on the controller flashes. The brakes do not appear to function at all aside from the one that stayed locked up. We replaced the 6pin on the trailer with a new 7blade. Took the truck end of the plugs apart to check for water, nothing. No apparent corrosion.

We are about to pull our hair out.

[Underthebridge]

I am having similar issues with my Chevy, check your fuses under the hood.
I hooked up to another trailer and am pretty sure it is the truck,

my next step is to replace those larger fuses, at least now the messages have stopped but probably still have no brakes:(

other issues were fixed with replaced fuse 2 months ago.

[hosspuller]

Check the simple things… In a logical manner. First, ground … don’t rely on the hitch. A bad ground can creat all sorts of wonky results. the current is looking for a return path. a brake coil might be the least resistance.

Then truck … make sure the controller is delivering power to the brake wire. confirm the lights are at the proper pin. then trailer. …

[airhorse]

Find another trailer to plug into your truck, and another truck to plug into your trailer. Should at least tell you where the fault is. Poor ground can cause lots of issues.

[Equibrit]

Check that the pin assignments in the plug and socket match. It sounds like the Ford side of the socket does not match the trailer pins. ie; you may have running lights feed from the truck going to the brake wiring on the trailer, or similar.

[Hampton_Bay]

Any chance this could have something to do with the one brake that was continuously actuated? Will try swapping trucks and trailers today. We don’t have another 7blade trailer though. Will have to find one to borrow.

[cssutton]

[QUOTE=Hampton Bay;7624048]
We bought a 2008 f350 about a month ago. Engine was brand new, so now that we have a few miles on it we hooked up the trailer to check things out. This is where the fun began.

One brake stayed locked up. We ended up just removing that brake entirely because nothing else worked. Figured we would handle that later.

That’s when the “wiring fault on trailer” started. It didn’t do that when the brake was locking up. Sometimes it says wiring fault, sometimes it says trailer disconnected. The lights all work. When you hit the brakes, the red light on the controller flashes. The brakes do not appear to function at all aside from the one that stayed locked up. We replaced the 6pin on the trailer with a new 7blade. Took the truck end of the plugs apart to check for water, nothing. No apparent corrosion.

We are about to pull our hair out.[/QUOTE]

One brake stayed locked up.

Lights are normal.

It appears to me that this means that the wire to that brake is always getting current.

Maybe from a short, maybe not.

So the first thing to do is to get one of those little testers that has a sharp point on it for the hot side and a wire with a clip on it for the ground.

Put the ignition switch in aux. position.

Touch each connector in the socket with the sharp point to see what connector is hot. If it is a short, you will have two hot spots, one will be the connector socket that sends power to the trailer. This hot wire’s purpose is to give the trailer power to operate interior lights.

The other hot spot will be the brake connector and this would indicate that there is a short between those two wires on the truck side of the connector.

Or it may mean that someone hooked the wires up wrong and the wire that is hot when the switch is on is hooked to the brake socket.

The Ford book should show you which connection points do what.

Actually one of the first things to do is to touch all sockets with the sharp point with everything off and the switch in aux. Then turn on each item one at a time and find out which socket is hot with that on…lights, on then off, right turn on, then off, left turn on then off, brake lights on and then off.

Be careful not to let the point touch the wire that is hot when the switch is on and one of the other sockets when on, like for instance the lights. If you do you will blow a fuse and get to play detective finding it in the Ford system. A very annoying process until you have done it a few times.

Check each against the book…

You mention a red light when the brake is on.

There is no red light on the Ford factory brake system. So this means you have an after market brake controller, probably hooked up incorrectly by the previous owner.

Before you can find out why one brake works and the others do not, you will have to determine by the above steps if the juice is going to the correct places in the socket.

You did not mention whether the trailer is one you had and used regularly before this truck and with or without any problems.

[My_Two_Cents]

No answers. Just sympathy. Nothing more frustrating then electrical problems on trucks and trailers. Advice from cssutton sounds like a good place to start.

[McVillesMom]

Aren’t there 2 different 7-pin configurations? Are you sure the truck and trailer are wired the same? Wondering if that could be your issue…

[Hampton_Bay]

It’s a factory brake controller. The manual even covers the red flashing light above the gain number on the controller. I can’t off the top of my head remember exactly what it means, but it means something isn’t working.

Ran out of daylight today to tackle it with the voltage meter.

The truck is new to us. Of course the previous owner he no issues. Trailer had been used once with the 99f350 but had no brake controller. We bought one but never hauled with it before selling that truck.

I don’t know about different wiring configurations for the 7pin. When we retired it we followed the adapter we had bought that didn’t seem to want to stay connected tightly, or so we thought. All other controls work, so I doubt it’s improper wiring in the plug. If we had swapped wires one of the lights shouldn’t work,

[Underthebridge]

I have brakes again, messages still gone, had to lower the gain since brakes lock at hard braking.

[Tom_King]

When tracing wires to a trailer to see which wire does what, lights are obvious, but brakes are not. A way to tell if electric brakes are being activated is to have a helper hold a compass near the wheel about 4 inches above the hub. If the brake is getting current, the compass needle will point hard to the brake magnet.

Some trailer manufacturers are stupid enough to use their own unique wiring diagram, and color coding, which is different than most of the others on the road.

[Equibrit]

[QUOTE=Hampton Bay;7625275]
All other controls work, so I doubt it’s improper wiring in the plug. If we had swapped wires one of the lights shouldn’t work,[/QUOTE]

Not necessarily;

The 7 pin assignments are…
12V
Taillights
Left turn
Right turn
Ground
Brakes
Auxiliary

[cssutton]

t’s a factory brake controller. The manual even covers the red flashing light above the gain number on the controller. I can’t off the top of my head remember exactly what it means, but it means something isn’t working.

News to me.

I drove a 1208 F350 127,000 miles pulling a 4H trailer about half of that.

There was no red light.

I have a 1212 F350 with 63,000 on it and the computer says half the miles pulled the trailer.

So what you are going to need to do is to do as I said: Get a tester, see if any socket on the truck side is hot with everything including the ignition switch is off.

Then turn on one by one, ignition, turn signals, clearance lights, brake lights, etc., and check each location according to the book.

Your trailer should have a diagram in its owner manual and the contacts should be the same since auto and trailer manufactures have standardized. If not, you will have to get them to match.

But regardless, you are getting power where it is not supposed to be.

Maybe there was a red flashing light on mine…but I never saw it because all of my stuff is wired correctly.

Be that as it may, there is no easy way and you are not going to get a one minute solution from the internet.

You are going to have to test each contact one at a time and find out what is hot and what is not.

The trailer manual should tell you how to set the gain.

Sundowner says drive the truck at 25 to 30 MPH and hit the trailer emergency.

Raise the gain until the tires squeal.

Then back of one number at a time until they do not squeal.

You do not use the truck brakes during this test, only the trailer emergency brake.

Periodically test as the gain setting will change due to drastic changes in load, such as empty va. all the horses and gear you can stuff in it.

And brake wear.

[Hampton_Bay]

The red light comes when you test the brakes like described. Haven’t had time to test wiring yet. We both work long hours, and with a baby and 92 degree days, we haven’t made it out yet to test the wiring. It’s planned for tomorrow.

Trailer is a 99 mid south 4h with 12’ short wall. No owners manual and can’t even find anything online about mid south having made trailers. So no luck there unfortunately. We have a wiring diagram for the truck but nothing for the trailer.

[FloridaHorseman]

Please explain how you “removed” the offending brake. Completely removed the brake shoes? Cut the wire? Do you have brakes on all four (3 now) wheels or just brakes on 2 wheels of the same axle? What were you pulling the trailer with before you got the F350?

Before you get mired too deep in wiring diagrams or tearing into the plugs and connectors you should put the trailer back into the condition it was originally. That means hooking up the brake that was locking and putting all wires back to where they were. Then test for voltage to the other brakes while the one brake is locked up. All brakes should be on the same 12v circuit. Most brake controllers send the stopping signal to the trailer on the blue wire in the plug. However some trailers accept the brake signal with a black wire on the trailer side of the plug and use a white wire for ground. So with the brake pedal depressed or using the manual slide on the controller if you have voltage at the brake that is locking it up you should also have voltage at the other wheels. If the other brakes don’t engage they may be way out of adjustment, just like the one that locked up might have been over adjusted. Many trailer brakes are self-adjusting when the trailer is backing up and the brakes applied. Some require manual adjustment with a spade-like tool inserted in a slot in the dust plate. The wheels need to be jacked up to see if they’re adjusted properly by spinning them and feeling or hearing a slight drag of the brakes against the hub with no voltage applied. But you first have to establish there is voltage getting to all the magnets. The compass test as previously suggested is a good one.

To further confuse the wiring issue some trailers are wired in a pattern called “RV wiring” while others are wired in a boat trailer configuration. The wiring pattern in the truck plug has to match one or the other. It will not operate both. And some model years Ford and Chevy were also wired differently. But to get to the heart of the problem you really need to work from the trailer forward. If all the lights function properly find out what color trailer wire is activating the brakes, trace it back to the trailer plug and see what it mates up to inside the F350 plug. My guess is you’ll find a hot red wire on the truck side. That should be AUX power to charge a trailer battery, if the trailer is so equipped. If not, make certain the red wire doesn’t connect to anything in the trailer plug. Find the blue wire on the F350 side and make sure it mates with whatever wire is running to the brakes in the trailer plug. It’ll probably be black but go with whatever color you find powering the brakes. Don’t choose the wire color coming out of the brake hub. Choose the color upstream of where the brake magnet wiring is spliced into the trailer wiring. ~FH

[Hampton_Bay]

We only removed the brake shoe, no wiring. Nothing else was changed aside from swapping from the 6pin to a 7blade. Current truck won’t take a 6pin and the adapter kept wiggling loose. We pulled the trailer once with a 99f350. No issues with it but it didn’t have a brake controller installed.

After a long evening where no lights worked, a blown fuse, compass worked, still have issues, we think the plug is still coming loose. If you hold the plug in, everything works. Otherwise the faults come and go.

[Mango20]

When I had an electrical problem I couldn’t figure out, I finally took the truck & trailer to a large RV service place. About 1 hour and $100 later, problem was solved. It was totally worth it.

[cssutton]

After a long evening where no lights worked, a blown fuse, compass worked, still have issues, we think the plug is still coming loose. If you hold the plug in, everything works. Otherwise the faults come and go.

You never mentioned a loose plug in your original post.

What a waste of everyone’s time.

[Guilherme]

Follow the advice of Equibrit and csutton. Get the adapter wired correctly for your truck and trailer.

After you do this you may find that you have another issue(s). That’s what makes truck/trailer electrical work so “thrilling.” ;(

You may, in the end, have to take it to a shop and get them to set it up correctly and run some tests. That’s an SUX because it costs money. It’s a Good Idea because they have to do it in 92 degree heat.

G.