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Old 04-20-2017, 05:28 PM   #1
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Default Trailer brake help needed.

Hey guys. I have a trailer with strictly electric brakes. It's a brand new trailer and the brakes seem to be fine on the trailer end. If I pull the emergency release cable they lock up. If I use a 12v source and touch the trailer cable in the 2 correct spots the brakes lock up.

Here's where I am lost. I have a 02 F-250 with the factory tow harness. Factory brake controller harness and a new Prodigy controller (I bought this as I believed the Reese one I had was the issue). When the trailer is plugged to the truck the brakes do not function. When it's hooked to the truck and I pull the safety cable they will not lock. With the safety pulled and then I unplug the 7-pin connector the brakes will lock. If I plug the 7-pin back up the brakes stayed locked.

On the truck, at the plug, when the box is turned all the way up and brake pedal pushed I get a +11.7v reading using the trailer ground pin and trailer brake pin. Voltage drops as it should when I lower the setting on the controller.

I've checked and made sure everything is grounded well. I made a jumper wire from the truck plug ground to ground to the pigtail and used another jumper in the trailer brake slot from the trailer. Now here's where I'm stumped and maybe it's something common. With the control box turned all the way up and the brake pedal pressed, the trailer brake terminal and both left and right brake light terminals have 11.7volts with the multimeter. If I touch the brake jumper wire to the trailer brake terminal on the truck nothing happens. If I touch it to either of the brake light terminals the brakes engage. All 3 have + voltage. What am I missing?
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Old 04-21-2017, 05:07 AM   #2
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Quote:
Originally Posted by DeclansDaddy View Post
the trailer brake terminal and both left and right brake light terminals have 11.7volts with the multimeter. If I touch the brake jumper wire to the trailer brake terminal on the truck nothing happens. If I touch it to either of the brake light terminals the brakes engage. All 3 have + voltage. What am I missing?
Did you check if you still have 11.7 volts on the trailer brake terminal when it is hooked up to the trailer or while it is jumpered? If not, check that. Your voltage may be dropping as soon as you hook up the trailer or touch the jumper to it.
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Old 04-21-2017, 06:45 AM   #3
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Not saying this is the problem, but, check the back side of the truck's 7 way plug, underneath the back bumper. The wire harness plugs in to the back of the 7 way plug and can get dirt in it or shake or break loose.
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Old 04-21-2017, 07:38 AM   #4
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After doing a little more research I also found this:

===============

When you stop at red lights, or any time that your truck and trailer are at a standstill with the brakes applied for more than 5 seconds, the Prodigy's "hold" feature will activate. When this happens, the power output to your trailer's brakes will be reduced to just 25 percent of the preset power setting so that the brakes will not overheat.

------------

Adjusting the Power to the Trailer
...
3. Drive tow vehicle and trailer on a dry level paved
surface at 25 mph and fully apply manual knob.
✓ If trailer brakes lock up:
❑ Turn power down using power knob.
✓ If braking was not sufficient:
❑ Turn power up using power knob.
4. Repeat Step (3) until power has been set to a point
just below wheel lock up or at a sufficient force as
to achieve maximum braking power
===============

Besides only applying 25% power after being at rest for more than 5 seconds it also senses inertia so it would need to sense deceleration to apply full power. 25% may be enough to "hold" your brakes, as it did in one of your tests, but probably not enough to initially suck the magnets to the drum and apply them. "With the safety pulled and then I unplug the 7-pin connector the brakes will lock. If I plug the 7-pin back up the brakes stayed locked." Try the "test drive" procedure.
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Old 04-21-2017, 07:56 AM   #5
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I have an 01 F350. After many hours of trouble shooting, I found that my truck didn't come from the factory with a certain fuse in the fuse box. I wish I could be more specific, but my friend who helped with this is out of town right now. It was an easy fix once discovered.
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Old 04-21-2017, 02:30 PM   #6
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Had the same thing happen with an '04 F250. After replacing the electro/hydraulic unit, and about to tear the 7-pin connector apart, found a blown fuse in the truck. It's a bigazz 40a I think under the steering wheel.
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Old 04-21-2017, 06:09 PM   #7
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Quote:
Originally Posted by jhackl View Post
Did you check if you still have 11.7 volts on the trailer brake terminal when it is hooked up to the trailer or while it is jumpered? If not, check that. Your voltage may be dropping as soon as you hook up the trailer or touch the jumper to it.
This seems to be exactly what happens I just don't know why.
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Old 04-21-2017, 06:14 PM   #8
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Quote:
Originally Posted by Rebelwarhorse View Post
I have an 01 F350. After many hours of trouble shooting, I found that my truck didn't come from the factory with a certain fuse in the fuse box. I wish I could be more specific, but my friend who helped with this is out of town right now. It was an easy fix once discovered.
Yea it's a separate relay box. My truck came with it already in it but I know some don't.
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Old 04-21-2017, 06:16 PM   #9
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Quote:
Originally Posted by Ray KSUSA3 View Post
Had the same thing happen with an '04 F250. After replacing the electro/hydraulic unit, and about to tear the 7-pin connector apart, found a blown fuse in the truck. It's a bigazz 40a I think under the steering wheel.
I checked fuses but worth a double look. Thanks.
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Old 04-22-2017, 11:25 AM   #10
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Quote:
Originally Posted by DeclansDaddy View Post
This seems to be exactly what happens I just don't know why.
Check the voltage coning out of the back of the controller when the trailer is hooked up and the brakes applied, usually this is the blue wire. If the voltage does not drop there but is dropping at the trailer plug then you have a problem with your wiring between the controller and the plug at the rear of the truck.

If the voltage does drop on the blue wire at the back of the controller when the brakes are applied, check the voltage going into the back of the controller with the brakes applied, should be black. If the voltage on the black wire drops then you have a problem with the power supply wiring to the controller.

If the voltage does not drop on the black wire but drops on the blue wire when the brakes are applied then this is internal to the controller and may be by design. You may have to actually be moving and decelerating to a stop for the controller to sense deceleration and apply full power to the brakes.
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