TT Brakes

3/4/2018 – Got it to power up. The Maxi-fuse 30 amp in position 1 was blown. The locations of the fuse below were all wrong. The advice to look at the Owners Manual was the best advice as that cites the correct location.

To get everything powered, you have 4 things you have to add/replace under the hood. In the main power distribution box, there are 2 30-amp “maxi” fuses (I think #16 and #28 (maybe 38) that have to be present. Number 16 enables the auxiliary 12V line for charging a trailer battery (usable if you have a 7 or 6 pin trailer connector). Number 28 runs the electronic brake controller power circuit and that is what is probably missing or dead.

You will also see under the hood, right next to the master cylinder and adjacent to the power distribution box, 1 or 2 smaller relay boxes. You will have 2 boxes if your truck is 4×4 and ESOF. In that instance, the box closest to the front of the truck holds 2 relays that run the electric shift motor in the NVG 273 transfer case. The small box closest to your firewall is the one you want. It probably is missing 2 relays. In the onwers‘ manual, these are numbered 38 and 39, but they are not numbered under the hood. Those 2 relays run the trailer backup lamps and the trailer battery charger (you have to have both the #16 fuse and this relay present to get the aux. 12v to work.

Inside the cab, make sure #13, a 20 amp mini, is present. I’m sure it is, or your cruise control wouldn’t work, but it also runs the trailer stop lamps. Check also #28, 10 amps. It energizes the relay under the hood for trailer backup lamps, among other functions.

When I did mine a year ago last May, I ran into two issues. The first was that you do need the fuse relay in block 28 in the panel under the hood. The second was that the wiring diagram that came with my truck when I ordered it was not totally correct for the Prodigy 3 controller I installed, with the ‘factory harness’ attachment. Once everything was in correct order, I had brakes to the trailer. The only thing that bothered me was that the controller stays on for up to 10 after you shut off power to the truck and trailer. I don’t know why they built this in to the controller, but it doesn’t have any adverse affect on the truck batteries. I can look tomorrow to see if I still have the wiring diagram, if you still haven’t sorted it out. What controller are you installing?

Have a ford f250 super duty what # is the fuse i need to ck Also is it under the hud or under the dash thanks

asked by: B D

Expert Reply:
You will need to locate the vehicles power distribution box and the trailer tow relay block attached to it. This is under the hood on the driver side. You will need to open the cover to access the fuses.

The information for where the fuse locations are will be in the owners manual of your vehicle or even if there is a legend on the fuse box cover you can use that. You will be looking for the trailer tow electric brake and trailer tow battery fuse locations. For the relays you will be looking for the trailer tow backup lamp relay and trailer tow battery charge relay locations.

The Trailer Tow Backup Lamp Relay is position #38 in the power distribution box. The Trailer Tow Charge is position # 39 in the power distribution box.
Brake Controller relay/fuse
I’m trying to help out my dad with his 2001 Screw F150 and brake controller wiring. I have a 2003 Screw, so I can look at mine to compare.

His came with the tow package, but I suspect they didn’t include the relay/fuse/pigtail with it. He bought the truck used and it has 100k miles on it. So I’m sure that kit is long gone.

He bought the pigtail and wired in the controller to the connector under the dash, but the controller doesn’t have the hot feed going to it. I suspect it’s missing the fuse and relays that are supposed to go under the hood. Can anyone tell me what fuse position is needed and what relays are needed?

Join Date: Oct 2005
Location: Louisville, Kentucky
Posts: 2,202

In the battery junction box (BJB) under the hood, there are three relays associated with the trailer wiring. K355, K356, and K357.
K355 Battery Charge Relay (Full relay)
K356 Parking Lamp Relay (Half relay)
K357 Reversing Lamp Relay(Half relay)
Fuses are in the BJB too.
F101 30A
F108 30A
F5 20A
rb848, please check your owners manual! Besides the harness, my 2000 F-250 needed two Maxi fuses and two relays to get power to the brakes/controller (blue) and power to the battery charge (black). Fuses went in the box under the hood and relays went into a small box beside the under-hood fusebox.
no-power issue with a Tekonsha Prodigy brake controller in my 2001 F350 SD 7.3L. —–I just went through this on my 2001. Wired up w/Ford harness,thought that was problem,bought another direct wire harness-no power. Under the hood on the left rear towards the cab theres a fuse box, there 2 Maxi fuses for trailer brakes, 30amp I think-there blue, there is 2 missing from the factory. One powers the brake controller and the other sends a charge to the trailers battery to keep it charged while truck is running. Plugged in and it works, theres 2 diff. pages in your owners manual that covers fuses,one for the inside box and other for under hood box.