Service trailer brake system

[massbowtie]

This is a long post,please bear with me.

Ok so my truck was in the body shop ,they removed the rear bumper and they put the bumper back on after they worked on it . I found the connector for 7 pin trailer plug was not connected for several weeks, meaning it was in the weather(corrosion). I ended up replacing the plug ,replaced with.aftermarket (hopkins). First time connecting the trailer, when i stepped on the brake ( i got a service trailer brake system) warning on. the d.i.c. I didnt look into at it until l iwas back home. I ended up towing with no trailer brakes. I double checked the connections they seemed ok.everything was working but the trailer brake. Not sure what happened i checked all the fuses that had anything to do with tail,park and brake lights and  i took them out and did an ohm test and they were all good. There is no power on the trailer brake wire(blue wire). I also found that now the truck brake lights only work when the key is on in the run position. Only other thing I did was wiggled the brake light switch and still no brake lights unless key is on, Did a search and found some people said it was either the brake light switch at the pedal or a sensor that is mounted on the master cylinder. I dont want to just throw parts at it and hate the idea of going to the dealer, just yet that is because . Im thinking its the brake light switch seeing the lights dont work and no power going back to the plug. Any help would greatly apreciated. Im supposed to haul the trailer in another week and would like to have trailer brakes working.

Thanks in advance. 

Mike

Billerica Ma.

[Doug_Scott]

The brake lights on my 2010, my buddy's 2012 and his sons 2012 do not light up unless key is on.  Shutting the truck off with foot on brake turns brake lights off as well.  All three trucks have trailer package, and all three have removable brake controllers with the controller not in place normally. 

Edited April 27, 2018 by Doug_Scott

[Jsdirt]

If I remember right, there's a big fuse in the under hood  fuse panel that runs the brake power - 40A I believe. There's also a wire to the front of the box that should be mounted to one of the studs there (battery + through that 40A fuse). When I first got my '07, that wire was taped up  under the brake booster - had to untape the harness and hook that wire up to the stud. Already had the eyelet on the wire for that.

 

Do you have the factory brake controller, or an aftermarket unit? It's possible that they shorted the brake wire and either blew the fuse, or smoked the controller.

 

The brake light thing was one of the first things I noticed when I first bought the truck. Only work key on, unlike any other vehicle I've owned the past 30 years.

 

EDIT: The "big" fuse was something I installed. It's supposed to be one of those newfangled cube fuses - AKA, a J-case fuse.

Edited April 28, 2018 by Jsdirt

[Doug_Scott]

57 minutes ago, Jsdirt said:

If I remember right, there's a big fuse in the under hood  fuse panel that runs the brake power - 40A I believe. There's also a wire to the front of the box that should be mounted to one of the studs there (battery + through that 40A fuse). When I first got my '07, that wire was taped up  under the brake booster - had to untape the harness and hook that wire up to the stud. Already had the eyelet on the wire for that.

 

Do you have the factory brake controller, or an aftermarket unit? It's possible that they shorted the brake wire and either blew the fuse, or smoked the controller.

 

The brake light thing was one of the first things I noticed when I first bought the truck. Only work key on, unlike any other vehicle I've owned the past 30 years.

 

EDIT: The "big" fuse was something I installed. It's supposed to be one of those newfangled cube fuses - AKA, a J-case fuse.

The big fuse supplies power to the trailer battery. GM provides both wires for trailer wiring at the engine fuse box.  Both wires have the Eyelet, and they have different size eyes to prevent you from hooking them up to the wrong posts on the front of the fuse panel box. I was surprised at how far they went with the "rough in" for the brake controller and trailer power on the 7 pin connecter.  Now if the different brake controller companies would just settle on a standard plug it could be made very easy instead of just easy. 

[massbowtie]

I could have sworn the brake lights would work with the key in the off position. I could be wrong. The wires for the trailer brake and 12 volt feed to the trailer have been hooked up for years and have power. I did check the 30 amp fuse and it was good. Today im going to look at the relay and another box above the spare tire. There are some people that found corrosion on the plugs and others say they had to replace the relay. Im not worried about the brake lights working when the key is off as long as it doesnt interfere with my trailer brake working. Everything worked before the body shop left the plug hanging in the  winter weather while I was plowing. I hate letting anyone working on my truck because of things like this.I will reply back with what I find if I dont shoot it and put it to the pasture.lol  Maybe I will get a new truck now instead of waiting another year or 2. Im not liking the looks of the 2019's at all. Thanks for the tips.

[massbowtie]

  I forgot to say I do have the factory brake controller.

[Doug_Scott]

Took me a couple of years to even notice, and that was when my buddy also found out because I check his to see if mine was broken. 

If you ever want to drive someone who has a car with shared brake and signal bulbs nuts put the left signal on with the key off and have him check the brake lights.  If he never notices the signal lever being on he will spend a lot of time trying to figure out why the left brake light is not working.  You can see this effect quite often on Barrett-Jackson auctions. GM fixed that by killing brake lights with key off or out. 

[massbowtie]

23 hours ago, Doug_Scott said:

Took me a couple of years to even notice, and that was when my buddy also found out because I check his to see if mine was broken. 

If you ever want to drive someone who has a car with shared brake and signal bulbs nuts put the left signal on with the key off and have him check the brake lights.  If he never notices the signal lever being on he will spend a lot of time trying to figure out why the left brake light is not working.  You can see this effect quite often on Barrett-Jackson auctions. GM fixed that by killing brake lights with key off or out. 

So yesterday I confirmed with another 2009 gm. Yes they do not work inless the key is on. I have checked fuses again. All is good there. I went to the relay and module connections and there was no corrosion none found thwy were dieelctric greased. I ohmed the wire from the plug and comfirmed the wire was good back to the relay and it was good.  I also read that the voltage at the plug shoulg between 3.1 and 4.2 volts. It has 3.6 volts. So my original problem.still exists (service trailer beake.system). Im at a loss. The.provisions for the trailer pkg. came.with.wires  so you could add a 7 pin plug in the bed for a 5th wheel.connection. i think its above the gas tank somewhere above the gas tank. Looks.like I might have to find it. Does anyone where abouts that might be ? If I do it and can check it and find no problems  then my next thing will be to replace.the.relay. any other ideas ? Climbing.under now to investigate more.  I have to tow next weekend and it.might be with no trailer brakes. Agravating.to aay the least because it all started.with moisture on the.7.pin trailer.wires. body shop told me to take it to the dealer on my dime,nice huh ? Off I go.

[Jsdirt]

Are you sure the problem isn't with the trailer brake wiring on the trailer itself?

 

The voltage output to the blue wire from the plug is going to vary based on your controller settings - higher settings = higher voltage (harder brake application), and vice versa.

 

Just FYI - wire resistance checks can throw you sometimes. A great example would be if only ONE strand of wire were connected in that circuit. Of course the ohm meter would read low or no resistance, since there's a connection ... but run 4-5 amps through that, and that tiny strand will quickly heat up, causing high resistance, more heat, and failure of the load to have enough available power.

 

Best way to test a wire is dynamically - a halogen bulb or sealed beam headlamp is an excellent test light. They draw roughly 5 amps. If the circuit can handle that, it will handle the load it's designed for, confirming wiring integrity 100%.

[massbowtie]

54 minutes ago, Jsdirt said:

Are you sure the problem isn't with the trailer brake wiring on the trailer itself?

 

The voltage output to the blue wire from the plug is going to vary based on your controller settings - higher settings = higher voltage (harder brake application), and vice versa.

 

Just FYI - wire resistance checks can throw you sometimes. A great example would be if only ONE strand of wire were connected in that circuit. Of course the ohm meter would read low or no resistance, since there's a connection ... but run 4-5 amps through that, and that tiny strand will quickly heat up, causing high resistance, more heat, and failure of the load to have enough available power.

 

Best way to test a wire is dynamically - a halogen bulb or sealed beam headlamp is an excellent test light. They draw roughly 5 amps. If the circuit can handle that, it will handle the load it's designed for, confirming wiring integrity 100%.

I dont have any trailer connected to the truck. I have a bar mashing the brake as hard as hard as it can be pushed. Im checking with the key on as well. You say to run 4 or 5 amps do you mean 4 or 5 volts ? I have tested with a test light and have comfirmed it has a good ground on the clamp side of test light. I would like to find the wores for that in bed 7 pin 5th wheel plug. Unfortunately the bolts on the tank straps are pretty rusty and want to snap them, dont need . As far as tunning 4 or 5 amps (volts) how do i regulate that low of a  pos. feed ? Bottom line the trailer brake warning is still on. Im still checking. Im going to go back to the control itself and look for chaffed wires, that is another possibility. Tips are great, thanks .

[massbowtie]

I have the controller gain set at 10.0 , the highest it goes with brake pedal mashed to the floor 

[Jsdirt]

I meant Amps. That's how we test circuit integrity. I should have mentioned that the circuit needs to be isolated for this test, and a power source supplied. If you don't do this type of testing every day, you might not know that.

[Jsdirt]

1 minute ago, massbowtie said:

I have the controller gain set at 10.0 , the highest it goes with brake pedal mashed to the floor 

Should be seeing at least 10v at the plug in that case - anything close to that would work (say 8-12v).

[massbowtie]

I dont get why a wet plug on the 7 pon could cause a chaffed wire. Maybe a wet wire or 2 shorted with water and popped the relay ?

[Jsdirt]

Wetness won't cause chaffing ... but a wet, already chaffed wire will short, corrode, or reduce voltage.

[massbowtie]

2 hours ago, Jsdirt said:

Wetness won't cause chaffing ... but a wet, already chaffed wire will short, corrode, or reduce voltage.

So i went back to check some other stuff out. Im assuming they use a blue wire from the controller to the module

 At the controller from the blue wire im getting 5.1 volts. In the harness from the front of the truck into the module i have 5.1 volts going into the module on a blue wire. A blue wire that comes out of the module  is tied into the large blue wire, one end goes to the 7 pin plug and the other large blue wire goes into the relay so its 3 spliced wires, I get 0 volts from the blue wire coming into the relay as well.Unfortunately  the battery died setting off stabillitrak and check charging system an d check braking system on the dic. Im assuming because the battery only had 6.6 volts that set it off.  I dont have a meter that reads amps but I did use a test hut it doesnt light up even dimly. Im going to change the controller to say 5 or 6 and see if the voltage is any less than the 5.1 volts that I have now. Again I apreciate the help you have given me.