Hello everyone!!! New poster here.


I am having troubles with my brother's 2018 F350 6.2L XLT SuperCrew Long Box Trailer Brake Control Module.
The initial problem was no stop or turn signals on either side of the trailer. From what I understand it happened simultaneously. I have done numerous tests and research on what fuses are what and everything looks okay on the surface.
Fuse 42(F42) and fuse 65(F65) supply power to the TrlCM via F42[Yellow-Red] and F65[Red] wires. Both fuses are intact, verified with multimeter.
Yellow-Red wire has about 1 volt until you pull F42, it drops to about .8v
Red has 12.x volts
F42 location has 12.x volts on the hot side and .8 volts on the feed side.
I put a jumper onto the yellow-red wire at the TrlCM and ran it to me at the fuse panel under the hood so I could check voltage when the fuse was installed, as I have 12.x volts on the F42 hot pin when the fuse is pulled. When I install the fuse and watch the voltage, I get a reading from about 4~5v and an instant drop down to the 1v range.
I put a jumper on the module from the Red wire which had proper voltage and plugged into both connectors on the module and checked the 7pin plug for juice and I had signals and stop lights activating on my tester plug. I verified the lack of signal before this.
I feel like there could be an issue in the fuse block itself under the hood, or it could be along the wire harness that I believe runs below the rad to the drivers side and then through the fender in behind the upfitter fuse block.
Has anyone experienced this issue or know of a common spot to check along the wire harness at a secondary junction plug?
I am planning to look at the inside of the fuse box under the hood on the passenger side to see where F42 goes and for any corrosion inside.
If no issue is easily found I am planning to snip the YW-RD wire near the plug for the TrlCM and eliminate the stock feed.
Both the RD and the YW-RD wires are supposed to be constantly hot. I have verified this through a few sources including my 2021 F350 Platinum with the same TrlCM.

Any help before we cut the stock wire would be great! Thanks all!!

 

Can you clarify this as that says you have just a bad fuse…

 

Ouch…why are you numbering wires…

if there is a trailer control module in the truck it won’t fully activate unless the key fob is in the cab.

 

I verified the fuses with the multimeter and visually. I get a quick spike of power when inserting the fuse and it drops off. The fuse was the first thing we tried to replace

 

F42 is Fuse 42 which supplies power to the Yellow wire with Red Stripe.
F65 is Fuse 65 which supplies power to the Red wire.
Both wires supply power to the Trailer Brake Control Module constantly. The yellow-red wire supplied by Fuse 42 or F42 has a major drop in power when the fuse is inserted. When I pull the fuse out and check the F42(Fuse 42) hot pin I have 12.x volts.
With the fuse in under the hood at F42, at the plug under the dash I have 1volt. When I unplug the fuse I get .8 volt. We tried a new fuse

 

that is with the fuse out and checking the voltages of the pin themselves.

 

key was in ignition and turned to the on position. My Platinum was not powered or have the fob in the truck and I have full 12.x volt power to both wires

I apologize for the multi replies. I am just learning this forum stuff. first day here!!

 

What I would do is remove the clear cover on fuse 42, then put it back in and now you can measure both sides of the fuse. These battery fuse boxes are known for getting wrecked by water getting into them and it sounds like the 12v feed to the fuse can’t support any current. With the fuse cover removed you can see if you still have 12v or if it has dropped saying there is a problem in the fuse box itself.

 

That is an excellent idea!! I apologize if my initial message was confusing. I will get back to you over the next couple days when I can get his truck back and try removing that cover!! I was annoyed when those J case fuses came out and you cant test them like the blade fuses

 

Unfortunately, I don't have a shop to work in, and our weather has not been favorable unless you want to dress up like the kid from A Christmas Story, "I can't put my arms down!"
I came up with a temporary solution to get us through. I ran a fused(40A) wire direct from the battery and into the cab, put a protected female blade connector on the wire and plugged it into the corresponding tab for the Yellow-Red wire on the Trailer Brake Control Module. I utilized the original power supply through the harness for the Red wire and made a short jumper to connect the Red lead in the plug to the Red tab on the control module.
When we have some warmer weather, I will diagnose this issue further.
For now, we have working trailer brakes and signal lights.