No trailer brakes due to electrical issue

[timkitch]

My tow vehicle recently started losing connection to my trailer brakes, but only when I was in motion. Now, it has no connection, even when sitting still. All other 7 pin connections - turn signals, etc. - work fine.

Ram dealer said was the brake controller module - replaced, no change.

I had a neighbor connect his truck to my fifth wheel and his truck also says there's no trailer brake connection. I connected my tow vehicle to his trailer and my truck says it does have a trailer brake connection. I think this totally rules out any issue on the truck side, including the likely suspects - e.g. brake module, brake module fuse, truck 7 pin connector, etc. So, I know it's an issue with the cable or the fifth wheel.

I also used my multimeter to confirm that the 7 pin on the truck side does have voltage when the brakes are applied. My trailer 7 pin cable has the type of connector that lets me remove a screw to access the back side of the plug, right where it connects to the truck. I tested the wires on the plug right at the truck. That showed NO voltage when the brakes were applied.

So, that tells me that there IS voltage, but only when the cable is NOT connected. As soon as I plug in, the voltage disappears.

I suspected the brake wire (blue) at the wiring harness under the fifth wheel hitch. It's not that - all the wires in that bundle are really secure.

Recently had 2 different RV tech re-secure the wiring under the fifth wheel at the brake drums and I re-checked those. Called one of those RV techs and all he had to offer was "replace the entire 7 pin cable". Seems like someone should know how to actually diagnose something like this (um, like an RV tech).

Any suggestions, other than me just changing out this and that?

Thanks in advance!
Tim

[Quantum]

Originally Posted by timkitch

My tow vehicle recently started losing connection to my trailer brakes, but only when I was in motion. Now, it has no connection, even when sitting still. All other 7 pin connections - turn signals, etc. - work fine.

Ram dealer said was the brake controller module - replaced, no change.

I had a neighbor connect his truck to my fifth wheel and his truck also says there's no trailer brake connection. I connected my tow vehicle to his trailer and my truck says it does have a trailer brake connection. I think this totally rules out any issue on the truck side, including the likely suspects - e.g. brake module, brake module fuse, truck 7 pin connector, etc. So, I know it's an issue with the cable or the fifth wheel.

I also used my multimeter to confirm that the 7 pin on the truck side does have voltage when the brakes are applied. My trailer 7 pin cable has the type of connector that lets me remove a screw to access the back side of the plug, right where it connects to the truck. I tested the wires on the plug right at the truck. That showed NO voltage when the brakes were applied.

So, that tells me that there IS voltage, but only when the cable is NOT connected. As soon as I plug in, the voltage disappears.

I suspected the brake wire (blue) at the wiring harness under the fifth wheel hitch. It's not that - all the wires in that bundle are really secure.

Recently had 2 different RV tech re-secure the wiring under the fifth wheel at the brake drums and I re-checked those. Called one of those RV techs and all he had to offer was "replace the entire 7 pin cable". Seems like someone should know how to actually diagnose something like this (um, like an RV tech).

Any suggestions, other than me just changing out this and that?

Thanks in advance!
Tim

I had to troubleshoot the trailer brakes on my most recent trip with my 2021 F150. Turns out, Ford just issued a recall for my brake controller, but at the time, I didn't know that was the issue.

So having just gone through this, at a South Carlina rest area, I would suggest starting with the following. Hook up the trailer but leave the 7-pin disconnected. Then pull the emergency breakaway cable on the 5th wheel and hop in the truck and try to pull forward. The trailer brakes should be locked up. If not, there is an issue with your trailer wiring.

When I performed the above step, I ruled out my trailer as the problem, because my brakes locked up when I pulled the pin.

[dxrobertson]

Originally Posted by timkitch

I also used my multimeter to confirm that the 7 pin on the truck side does have voltage when the brakes are applied. My trailer 7 pin cable has the type of connector that lets me remove a screw to access the back side of the plug, right where it connects to the truck. I tested the wires on the plug right at the truck. That showed NO voltage when the brakes were applied.

So you test the truck side plug/socket trailer brake pin (trailer unplugged) with the meter ground attached to truck side ground, apply brakes; and get voltage, correct? good.

Then you plug in the trailer plug with the cover pulled back to access the wires and connections on the trailer side. Test the brake wire at the trailer plug, apply brakes; and get no voltage? This is just on the backside of the trailer plug thats plugged right into where you just tested the truck and had voltage? Where is the meter GROUND connected? Try connecting meter ground to a TRUCK GROUND (pos meter probe still at exposed trailer brake wire). Now what happens? This tests the plug connection and the trailer brake wire at the plug, nothing else.

If no voltage, I'll have to think about that.

Also, unplug and run an ohm meter test from inside the trailer plug brake connection to the wire connection the other side of trailer plug where you pulled the plug cover back, trying to connect this side to the stranded wire itself.

[Rustic Eagle]

I had a similar problem...., wire running through one of my axles was shorting out due to rubbing against the inside surface of the axle.



Reference Post #235 here: https://www.jaycoowners.com/forums/f...-51005-13.html

Bob

[dxrobertson]

Originally Posted by Rustic Eagle

I had a similar problem...., wire running through one of my axles was shorting out due to rubbing against the inside surface of the axle.



Reference Post #235 here: https://www.jaycoowners.com/forums/f...-51005-13.html

Bob

Makes sense. A grounding out issue would probably cause a breaker back on the truck side to throw, thus no 12V at the plug when plugged in and brakes applied.