Tekonsha P3 goes to 0.0 when stepping on the brakes

[Poodlehead]

Hi,

I'm new to trailer brake controllers and need a little guidance.

The main cord pulled out of the 7 pin shroud so I disassembled and put it back in. I assumed it would go only one way so I didn't pay close attention when dis-assembling it. I think I may have put it back together 180 degrees opposite.

All the lights and blinkers work, but when I step on the brakes, it shows 0.0 and the brakes release as expected. When I take off, the numbers jump around from .4-1.5 and everything in between until I step on the brake. Then it goes to 0.0 and the brakes release.

I'd go ahead and swap it back ari, but I'm concerned I might have it in properly now and really make things worse by swapping it.

Any input is greatly appreciated! TIA! Pat

 

[Bill]

Pat -

If the brake lights, running lights, and blinkers work as expected, there is no rotation of the connector core itself. Did you re-connect any of the individual wires within the connector? That could bring some pretty screwy results.

Do you have access to a voltmeter (VOM, DVM, etc) or an automotive test light? We can check the basic functions coming through the connector pretty quickly.

What is your tow vehicle? I seem to recall that a few European vehicles (VW?) don't adhere to the standard wiring format. Who installed your P3?

I'm a bit confused by your statements that the brakes release when you step on the pedal. The brakes should apply, not release, when you step on the pedal. Can you clarify before we go on?

Bill

 

[Poodlehead]

Thanks for the response!

My tow vehicle is a 77 Chevy truck. I installed the connector myself and it was working properly before, except one wheel gets hotter than the other side (that's another problem that I still have to resolve).

When I step on the brake pedal, the controller goes to 0.0 and the trailer brakes release, just as the 0.0 indicates. When I take off and the numbers jump around, I can feel the brakes engaged until I tap on the brake pedal. Then I can feel the brakes release and the controller shows 0.0

I do have a VOM, but my gut tells me that I may have put the shroud on backwards. I'd swap it around, but I really don't want to create new problems...

 

[Poodlehead]

And no, I did not reconnect any individual wires when I pulled the housing off. I just pushed the main cable back in to strain relief it again.

 

[Bill]

Pat -

On the end of the TM cord, the core of the TM connector is keyed into the shroud, and the shroud is keyed into the shell of the truck's mating connector. If true, neither can be accidentally rotated. Besides, if the connector was rotated 180 degrees, the lights wouldn't work correctly. For example, the connector pin carrying the left-turn signal is opposite the pin carrying the right turn signal. If the connector is rotated 180 degrees, the TM's turn signals would be reversed. So based on what you have told us, that ain't it.

My best guess is that the P3's black (+12VDC supply) and red (brake pedal sensor) wires are interchanged. That would cause at least some of the weird stuff you are seeing.

The other possibility is that the P3's red brake-pedal sensing wire is connected to the wrong side of the truck's brake light switch. Easy to do. If I recall correctly, when the brake pedal is up, one side of the switch is hot and the other side is cold. The P3 should be connected to this cold side. When you push the pedal down, the previously cold side goes hot, signalling to the P3 that you are applying the brakes. If you connect the red wire to the always-hot side of the switch, the P3 thinks the brakes are always being applied. Among other things, this would cause a hot brake, which you are seeing.

My suggestion is to review the how the four wires from the P3 are connected into the truck wiring.

Two other questions.
1. When the P3 was installed, was a self-resetting circuit breaker part of the installation?
2. Was a 4-pin-to-7-pin adapter involved in your installation?

Bill

 

[Poodlehead]

Bill,

I will double-check how I have the controller connected to the brake switch and if I have it connected to the 'hot' or 'switched' side of the brake switch.

I did not install any type of circuit breaker and I did not use a 4-7 pin adapter. When I bought the controller, it came with the 7 pin connector that I mounted just behind the rear bumper.

I'll update when I have more info. Thank you for your help/guidance.

Pat

 

[Poodlehead]

Bill,

I did some checking today and I'm starting to lean towards a bad brake controller.

I verified again that the brakes and turn signs are working properly.

I verified the red sensing wire is connected to the switched side of the brake switch. Also, since the controler does recognize when I step on the brake(0.0) that reconfirms it's connected on the switched side of the brake switch.

I monitored the blue wire and it has the same voltage reading that the P3 displays. The voltage value changes some, including when I shake the controller. Sometimes the voltage goes all the way up to the max value set on the controller of 4.5 volts.

The manual switch on the bottom does apply the brakes properly too. I didn't think to lightly step on the brake (to make it go to 0.0) and then actuate the manual switch, but I'm betting it will work properly.

The only other thing I can think of is the position of the controller when it's mounted, but since this time I had it in my hand and it made no difference.

The truck wasn't moving for any of these tests.

I left a message with their tech support about a month ago and no return call. Guess I will be calling again on Monday...

Circuit breaker - is that required for any specific reason if I am already pulling power from a switched 12v that is already fuse protected?

Thank you,
Pat

 

[Shane826]

The controller won’t apply much if anything if the truck isn’t moving because it doesn’t sense any deceleration. Shaking the unit would allow it to sense deceleration and maybe apply some power.

 

[Poodlehead]

The controller won’t apply much if anything if the truck isn’t moving because it doesn’t sense any deceleration. Shaking the unit would allow it to sense deceleration and maybe apply some power.

That's what I was trying to simulate a bit by moving/shaking the unit. When the unit is completely still, it still applies random voltage to the blue wire and display which I don't think is right.

I emailed tech support earlier today and hopefully I'll get a response from them tomorrow.

Thank you!

 

[Bill]

Bill,

I did some checking today and I'm starting to lean towards a bad brake controller.

I verified the red sensing wire is connected to the switched side of the brake switch. Also, since the controler does recognize when I step on the brake(0.0) that reconfirms it's connected on the switched side of the brake switch.

You are right - this is the expected response when the truck is not moving. Since there is no deceleration, the unit knows that it does not need to apply trailer brakes.

I monitored the blue wire and it has the same voltage reading that the P3 displays. The voltage value changes some, including when I shake the controller. Sometimes the voltage goes all the way up to the max value set on the controller of 4.5 volts.

Right again. When you shake it, it senses some random and varying deceleration, and applies brakes accordingly.

The only other thing I can think of is the position of the controller when it's mounted, but since this time I had it in my hand and it made no difference.

Most controllers specify that to operate as intended, they must be mounted facing straight ahead, level side-to-side, and level fore-and-aft within a certain (not large) amount. If you are holding it in your hand and shaking it, these conditions won't be met, so the response will be random, and won't tell you anything useful.

Circuit breaker - is that required for any specific reason if I am already pulling power from a switched 12v that is already fuse protected?

How big is the fuse? It shouldn't be a whole lot bigger than specified by Tekonsha, which I think is 20 amps. The other detail is that a fuse isn't self-resetting. If you apply the brakes and the fuse blows while braking, it won't reset, leaving you with no brakes for the next stop. By contrast, the circuit breaker will reset in a few seconds - not in time for the current stop, but in time for the next one (where it may pop again).

So at this point, I guess I am unclear about what the problem is. Can you rephrase, without reference to shaking it, holding it in your hand, exercising it when the truck isn't moving, etc?

Bill

 

[Bill]

I am homing in on these items from your first couple posts.

When I step on the brakes, it shows 0.0 and the brakes release as expected. When I take off, the numbers jump around ... until I step on the brake. Then it goes to 0.0 and the brakes release.

and

When I take off and the numbers jump around, I can feel the brakes engaged until I tap on the brake pedal. Then I can feel the brakes release and the controller shows 0.0

I'm trying to understand "release". We're not talking about the truck brakes, which are not involved - we are talking about the TM brakes. So my first question is how you know the TM brakes are set? With a reading of 1 or 2 out of 10, it would be hard to feel the braking. And then, how do you know when they release?

From the first quote, when you step on the brake pedal and the readout shows 0.0, that is what is expected to happen. But why are the brakes set in the first place? My only guess is that the truck's shift lever is originally in Park, and when you shift into Drive, there is a small lurch - which the controller interprets as a request for braking. So it provides some. OK, I don't see this as a problem.

But then it should drop quickly to zero on its own, since there is no more deceleration unless truck is quivering. A clue is that when you release the brake pedal, the numbers don't go to zero as they should, but jump around until you tap the pedal. These questions could be answered by a sticky brake switch in the truck. When you take your foot off the brake pedal, the switch is expected to switch off immediately, but perhaps it is a little gummy, and it takes a few moments for the actuator to rise. Not a surprise in a 50-year-old truck. The answer might be as simple as getting a little lube into the switch. Please don't use WD-40, a known gummer-upper. Instead, get some kind of Dry Lube in a spray can with a nozzle. Shoot it into the base of the actuator, and work the switch a dozen times. Any change?

Bill

Finally, I hesitate to mention it, since I am sure that you have mounted the controller facing in the right direction. If it were facing backward, then when you accelerate out of dead stop, it would interpret the acceleration as a DE-celeration, and apply the TM brakes.

 

[Poodlehead]

Bill,

Sorry for the confusion. I was trying to hold the controller and simulate movement while monitoring voltage, but that doesn't work too well...

I put the brake controller back in it's mount and went for a test drive. It's pointing fairly level, but the fore/aft are not perfect, due to limited available mounting spots. Maybe I need to make a special bracket to get it dead nuts level with the fore/aft in the perfect direction with the road??? If I was smart enough to attach a pic of the controller mount, but I guess I'm not smart enough to get it attached...

Blue wire voltage varies from 0.4V to 1.5 V when I accelerate and at steady cruising speed. When I push the brake pedal to slow down, the display goes immediately to 0.0V and stays there until I release the brake pedal. While the brake pedal is applied, the trailer brakes are NOT applied.

Red wire goes from 12V to 0V when stepping on the brake pedal.

I don't remember which circuit I tapped into for power so I'm not sure about the fuse size, but yes, I will add a self resetting circuit breaker once I get this other problem resolved.

Thank you,
Pat

 

[Poodlehead]

I am homing in on these items from your first couple posts.

and


I'm trying to understand "release". We're not talking about the truck brakes, which are not involved - we are talking about the TM brakes. So my first question is how you know the TM brakes are set, and then, how do you know when they release?

From the first quote, when you step on the brake pedal and the readout shows 0.0, that is what is expected to happen. But why are the brakes set in the first place? My only guess is that the truck's shift lever is originally in Park, and when you shift into Drive, there is a small lurch - which the controller interprets as a request for braking. So it provides the braking.

But at this point, it should drop quickly to zero on its own, since there is no more deceleration unless truck is quivering. A clue is that when you release the brake pedal, the numbers don't go to zero as they should, but jump around until you tap the pedal. These questions could be answered by a sticky brake switch in the truck. When you take your foot off the brake pedal, the switch is expected to switch off immediately, but perhaps it is a little gummy, and it takes a few moments for the actuator to rise. The answer might be as simple as getting a little lube into the switch. Please don't use WD-40, a known gummer-upper. Instead, get some kind of Dry Lube in a spray can with a nozzle. Shoot it into the base of the actuator, and work the switch a dozen times. Any change?

Bill

The "release" is the trailer brakes not being applied. I can 'feel' my forward motion getting easier when I tap the brake pedal and see the controller goes to 0.0V, so that is my guide.

Yes before I did have the truck in park, but it's not just the quick lurch making the numbers change briefly; it continues after the lurch...

I don't think I have a sticky brake switch since the red wire immediately toggles between 12V (13.4V actually) and 0.0V.

Thanks again,
Pat

 

[Bill]

Pat -

Aha! Just spotted something in the P3 manual that may be the answer.

"The P3 will “HOLD” your trailer with 25% of
power setting while you are at a standstill with
brake pedal applied for longer than 5 seconds"​

Could this why the reading doesn't drop immediately to zero? I never had a "hill holder", so I am not familiar with the details of the readout as it works.

Also, I was wrong about fore-aft leveling. The P3 will self-adjust to any level. Never experienced this either - neat!

Bill

 

[Poodlehead]

Bill,

That is new info that I wasn't aware of... Since the controller applies trailer brakes randomly while moving without the foot on the brake, I'm still thinking it's a bad controller???

l spoke with tech support this morning and he thinks I have a bad brake switch, even after I repeatably told him it switches from 12 - 0 when I tap the brakes. I may try TS again tomorrow...

Thanks!
Pat

 

[Poodlehead]

Well I spoke to tech support again and now I know what the problem was... The brake switch is normally closed, which is applying 12V to the red sensing wire on the controller, until you press the brake pedal. The signal from my brake switch needs to be inverted, so I just did that by installing a 12V relay. A short test drive shows it working correctly.

Then I wanted to go a step further and play with the manual lever on the bottom of the controller and possibly tweak the power setting.

When I did that, the 15A fuse for my 12V power to the controller blew. I am going to run a 12GA wire from the battery to the controller with a 20A circuit breaker installed near the battery, as you suggested.

When I installed the controller years ago, I missed that the red sensing wire needed 12V when the brakes are applied. I just ASSumed it was smart enough to sense the trigger from the brakes. That's what I get for ASSuming

Thank you all for your help!

Pat

 

[Poodlehead]

I looked at a wiring diagram and it looks like the idiot installer (ME) made a few mistakes installing the 7 pin connector years ago...

1. Blue wire size added between 7 pin conn and controller is too small - Not by much so may not matter???

2. Black wire was tapped into a 15A fuse at the fuse block and too small - I will install a 20A circuit breaker near battery with 12GA wire run to controller.

3. No connection between the battery/40A circuit breaker and the trailer connector - Brakes appear to work so is this wire needed?