Just rewired all the brake wiring in our TT to all #12 right up to the junction box in the A-frame. Recently installed the Prodigy P3 brake controller out of our old F250 in our "new" 2012 GMC Sierra 2500HD.Went for a test drive today and the TT brakes just aren't working right. When I pull the manual lever, the TT barely slows down. I jacked up all the wheels and pulled the breakaway pin. Brakes all work, but they're not clamped as tight as I thought they ought to be. Should it be possible to wiggle the wheels at all?I checked the output at the b/c with a voltmeter and am getting around 12 volts output with brake pedal depressed. Can also measure the same voltage at the 7-pin connector with pedal depressed. The thing that doesn't make sense is that when I go through the troubleshooting menu on the b/c, it says the output voltage is zero and current is about 0.4 amps or less. Is this because the truck isn't moving? but how can I be measuring the voltage on the output wire?Is there perhaps a ground issue somewhere or maybe bad splice in the junction box in the A-frame or dirty connection in the 7-pin connector? Tail lights, turn signals & running lights on the back of the TT work fine.The brake controller has been working fine up to now.Off to check the connections in the junction box and the ground to the frame...

Something isn't right. When I pull the breakaway pin, I'm only reading 10 volts at the splice in the junction box. Voltage at the AGM battery in the TT is reading 12.7 volts with the converter turned off so the battery is good. Need to do some more investigation but it's supposed to rain over the next 3 days.On top of this, the battery in the truck is dead now and I can't start it. I see it's got the original 7 year old battery so looks like it's due for replacement. Put a charger on it so at least can start it tomorrow and get a new battery.

Is there a chance that you have the brake leads reversed?Verify that the acuator wire is power and the ground is actually the ground. You could be sending the power from truck straight to ground.

enblethen wrote:Is there a chance that you have the brake leads reversed?Verify that the acuator wire is power and the ground is actually the ground. You could be sending the power from truck straight to ground.Good suggestion but I did check that. It's odd that I'm only seeing 10 volts in the junction box splices when I pull the breakaway pin (without truck connected). I'm wondering if the TT battery isn't grounded properly somewhere or there's a bad connection in a pos. connection. Battery is inside and thus no corrosion on the terminals.

Where is the brakes grounded?Have you tested the voltage right at the battery with break-away pulled? You need to trace the battery ground. Hopefully it goes to the frame and not just to the converter.

enblethen wrote:Where is the brakes grounded?Brakes are grounded at the A-frame. Few years ago, I installed two separate ground lugs to the frame (quality ones) and used stainless steel screws into the frame. One of the grounds is redundant in case one fails and connect together inside the junction box. That's were the brake cable is grounded. Should be well grounded there but will check.Have you tested the voltage right at the battery with break-away pulled? No, not yet but that's a good idea for sure.You need to trace the battery ground. Hopefully it goes to the frame and not just to the converter. Besides the grounds in the A-frame, there's a bare ground wire to the frame on one side. I removed the poor factory ground lug there a couple of years ago and installed a brass grounding stud designed for wet locations. Need to check that too.

TT brakes not working right - new truck & new wiring

20 Replies

myredracer
Explorer II
Jun 27, 2019
stallsmi wrote:
I had pretty much the same problem with my TT and a Ford F250. Turns out the problem was with the 7 pin connector on the truck. After having the brake controller checked, the brake wires completely re-done, I swapped out the connector and everything worked. I got a new connector from etrailer.com.
This is a thought I had too. The contacts in the truck's connector aren't corroded, but definitely dirty and were full of dust. There is a cleaner tool but is expensive and probably cheaper to just replace the connector. All the lights on the back of the TT work great though.

There's also some connector blocks at the rear bumper near the connector. Not sure if they're related to the 7-pin connector but also another possibility.
stallsmi
Explorer
Jun 27, 2019
I had pretty much the same problem with my TT and a Ford F250. Turns out the problem was with the 7 pin connector on the truck. After having the brake controller checked, the brake wires completely re-done, I swapped out the connector and everything worked. I got a new connector from etrailer.com.
BFL13
Explorer II
Jun 27, 2019
Some brake controllers have an "adapter" wire set needed, which is different for each brand of truck. No idea if this is the case here, but OP went from Ford to GMC.
JRscooby
Explorer II
Jun 27, 2019
myredracer wrote:

Went for a test drive today and the TT brakes just aren't working right. When I pull the manual lever, the TT barely slows down. I jacked up all the wheels and pulled the breakaway pin. Brakes all work, but they're not clamped as tight as I thought they ought to be. Should it be possible to wiggle the wheels at all?
.

As to the "wiggle"; When power gets to mag, the mag drags on drum. The rotation of the drum then the lever pry the shoes apart and to the drum. So if the wheel is not turning no brake is applied. So yes, a well working brake will let the wheel rotate a little.
First question reading your post; Have you adjusted your brakes? The I thought of the other thread. Poor connections might mean long time of light applications which can cause the shoes to glaze.
DFord
Explorer
Jun 27, 2019
An amp meter helps trouble shoot electric brakes. Maximum current draw should be just over 3 amps per magnet. just put a meter like this one in series with the magnet:

https://www.amazon.com/uxcell-0-10A-Rectangle-Analog-Ammeter/dp/B0050MQK16/
myredracer
Explorer II
Jun 27, 2019
enblethen wrote:
Where is the brakes grounded?Brakes are grounded at the A-frame. Few years ago, I installed two separate ground lugs to the frame (quality ones) and used stainless steel screws into the frame. One of the grounds is redundant in case one fails and connect together inside the junction box. That's were the brake cable is grounded. Should be well grounded there but will check.

Have you tested the voltage right at the battery with break-away pulled? No, not yet but that's a good idea for sure.

You need to trace the battery ground. Hopefully it goes to the frame and not just to the converter. Besides the grounds in the A-frame, there's a bare ground wire to the frame on one side. I removed the poor factory ground lug there a couple of years ago and installed a brass grounding stud designed for wet locations. Need to check that too.
enblethen
Nomad
Jun 27, 2019
Where is the brakes grounded?
Have you tested the voltage right at the battery with break-away pulled?
You need to trace the battery ground. Hopefully it goes to the frame and not just to the converter.
myredracer
Explorer II
Jun 27, 2019
enblethen wrote:
Is there a chance that you have the brake leads reversed?
Verify that the acuator wire is power and the ground is actually the ground. You could be sending the power from truck straight to ground.
Good suggestion but I did check that. It's odd that I'm only seeing 10 volts in the junction box splices when I pull the breakaway pin (without truck connected). I'm wondering if the TT battery isn't grounded properly somewhere or there's a bad connection in a pos. connection. Battery is inside and thus no corrosion on the terminals.
enblethen
Nomad
Jun 27, 2019
Is there a chance that you have the brake leads reversed?
Verify that the acuator wire is power and the ground is actually the ground. You could be sending the power from truck straight to ground.
myredracer
Explorer II
Jun 27, 2019
Something isn't right. When I pull the breakaway pin, I'm only reading 10 volts at the splice in the junction box. Voltage at the AGM battery in the TT is reading 12.7 volts with the converter turned off so the battery is good. Need to do some more investigation but it's supposed to rain over the next 3 days.

On top of this, the battery in the truck is dead now and I can't start it. I see it's got the original 7 year old battery so looks like it's due for replacement. Put a charger on it so at least can start it tomorrow and get a new battery.

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TT brakes not working right - new truck & new wiring

20 Replies

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