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

myredracer
Explorer II
Jun 29, 2019
Got myself a Curt UScar replacement "RV blade socket". Only $20. They're not GM specific like I thought. Will try a little delectric grease on it.
myredracer
Explorer II
Jun 29, 2019
BFL13 wrote:
Here is that colour code info--note the table for GM, Ford, and Dodge.

Drive you crazy matching with the standard 7-pin colours and the way the OEM is in two parts facing in the middle while the end of the outer part faces the trailer.

http://www.iegtoclub.com/Tech%20Lib/trailer_wiring_information.htm
Thanks for that! Below is a photo of what the GM plug looks like. It also has a connector/plug that connects the truck's wiring harness to the plug. So that's another set of contacts that can go bad. Not a great design electrically speaking. Going to try and find a new 7-pin plug and hardwire it into the harness instead and eliminate a potential source of a poor connection. To heck if I'm going to pay the GM dealer the $100 Can. they want for a new one.

There was a tag hanging off the harness near the bumper. Barely readable but can cross-reference it the info. you linked to.

RCMAN46 wrote:
The P3 has a whole host of diagnostic features. Such as it will tell you what the voltage and current that is being delivered to the trailer.

Have you used any of the diagnostic features?
Yes, have been using it for checking the output current and voltage. At first I was only getting about 0.4 amps, now I'm getting up to around 14 amp when I use the manual lever. What I'm not sure why is that the voltage still reads next to nothing while it looks okay at the back of the truck.

Yesterday I talked to Tekonsha and the tech. suggested using a 12 volt incandescent bulb right at the output of the b/c. That's when I was able to determine that the controller was working fine and it had to be the truck wiring.
RCMAN46
Explorer
Jun 29, 2019
The P3 has a whole host of diagnostic features. Such as it will tell you what the voltage and current that is being delivered to the trailer.

Have you used any of the diagnostic features?
BFL13
Explorer II
Jun 29, 2019
Here is that colour code info--note the table for GM, Ford, and Dodge.

Drive you crazy matching with the standard 7-pin colours and the way the OEM is in two parts facing in the middle while the end of the outer part faces the trailer.

http://www.iegtoclub.com/Tech%20Lib/trailer_wiring_information.htm
myredracer
Explorer II
Jun 29, 2019
Finally got it - something I overlooked from the beginning and didn't suspect.

When the 7-pin connector on the end of the pigtail was plugged into the female plug on the back of the truck, it wasn't making a connection even though the connector was locked onto the plug. Even when I push as hard as I can, it barely makes a connection on the brake circuit. So now I just need to get a new plug for the truck.

I also found one of the tabs inside the end of the pigtail connector was spread apart a bit and and I bent it back to where it should be. It was for the power to the brakes so that didn't help either. Might get a whole new pigtail & connector too

Once I get the new plug on the truck, I can do another road test and make sure it's all good. No big surprise, our local GM dealer wants 4 times the average cost on the internet for a new GM plug.
BFL13
Explorer II
Jun 28, 2019
You don't mention much about the display during all this. What does the display say for warnings etc?

https://www.tekonsha.com/support/installation/N90195.pdf

Not clear if there should be any output unless decelerating. (Proportional) ?

Something about no output if you have the brake light on ("stop lamp active") at the same time when you connected gets you a warning display.
enblethen
Nomad
Jun 28, 2019
Refresh my old brain cells!
My memory tells me that the brake light lead only supplies control power to the controller. There is a separate power feed to controller that actually supplies power to the trailer brakes.

wiring diagram
myredracer
Explorer II
Jun 28, 2019
After a day of checking things out, still not working. Took it for a test drive and still the same as before. The brakes on the rear axle are new and maybe they need a few miles to burnish them.

- checked all pos & neg connections and ground points to the frame on TT.
- few years ago I installed a shunt in the pos. from the battery near the converter for an ammeter but never mounted the meter. Removed the shunt.
- replaced the breakaway switch because it appeared to have corroded contacts and voltage wasn't what it should have been.
-replaced battery in the truck.

Pulling the breakaway switch appears to be making all 4 wheels brake okay and voltage is good at 12.4 - 12.5 volts.

The menu on the P3 is still saying output voltage is zero and current is only about 0.5 amp. The input voltage from the brake pedal is fluctuating quickly between about 12.5 & 14 volts. Maybe the switch needs replacing? Checked the wiring connections again between P3 and GM wiring and looks okay.

Think I'm just going to take it into the hitch shop and maybe they can figure it out quickly.
BFL13
Explorer II
Jun 27, 2019
myredracer wrote:
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.

Your 2012 is about the age when my 2003 Chev had trouble with the bumper 7-pin. It comes in two parts unlike the standard replacement ones you buy. Between the two parts was all corroded.

Replacing it with the standard one- piece took some effort because of the weird wire colours Chev uses. There is a diagram for that on the web somewhere--try Google. Also "mirror images" to figure out for which way the pins "face" with the two halves of the OEM plug going to the replacement.

The new one did not go on the OEM bracket so I have it strapped on the bracket in an ugly way.
myredracer
Explorer II
Jun 27, 2019
BFL13 wrote:
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.
GM stopped providing a plug a number of years ago and just provided some "cut" wires under the dash. I phoned Tekonsha to ask them. I still had the adapter plug with wire connectors at one end from when we bought the P3 two trucks and 7 years ago.

The P3 is all properly wiring according to the color coding. I did verify correct voltage from the brake pedal when depressed. I think what I need to do is solve first is why I'm only seeing 10 volts when I pull the breakaway pin.

It's raining hard today here and not to keen on crawling under the trailer today. Will at least go get a new truck battery. :(