Need Help With Brake Controller

Tage · January 30, 2008

I bought a used 20' enclosed trailer from a private party to tow my track/race car with. Obviously trailer brakes are a must for something this size. The trailer has electric brakes on both axles. I have a Tekonsha Prodigy brake controller in our GMC Yukon and the trailer brakes worked great for the drive home. On the drive home, it was quite obvious that the little GMC 5.3L V8 would not be up to the task of towing this trailer beyond just some local events.

So I bought a GMC Yukon XL with a 6.0L V8. I figured the longer wheel base and more weight would make for a more confidence inspiring vehicle while towing, additionally the extra torque from the bigger engine would make it more tolerable to maintain the speed limits and climb any of the hills. Everything seems to be fine except I can't get the brake controller to work! Install of a brake controller is a breeze since you simply plug the brake controller harness into the brake harness plug in this black box which is near the brake pedal. The harness port is even labeled and keyed you it's idiot proof!

Well I did the 1 minute install, hook up the trailer and immediately find out that something is wrong. The trailer won't move because the brakes are locked up??? The brake controller says the trailer is not connected yet the trailer lights all work. I unplug the brake controller harness from the GMC port and the brakes are still locked up. I have to unplug the round 6-7 pin connector near the rear bumper before the trailer brakes release. Strange??? I jack around with this for quite some time to no avail so I install the brake controller back in the original vehicle (we still haven't sold the original Yukon yet), hook up the trailer and now the brakes don't work in that vehicle either!

Now I'm getting way frusterated. Suspecting my plug converter from my trailer to my vehicle might be bad (<--brand new and recently replaced) I go to Autozone to grab another one to verify the pinouts and functionality and it's the same result.

At this point I know the following:

Yukon (old tow vehicle):

- The trailer brakes and controller worked at one point

- When hooked up, the trailer lights work but the brake controller says not connected

- I can drive hooked up but have absolutely no trailer brakes

Yukon XL (new tow vehicle):

- The trailer brakes and controller have never worked

- When hooked up, the trailer lights work but no matter what the trailer brakes are activated 100% (brake controller says not connected)

- I can't drive because the trailer brakes are locked up

So now I bust out the volt meter and check each pin out on the vehicle. All pins work/function as expected except for the pin that is labeled as a constant 12v source and the pin labeled as the brakes. On the Yukon, there is no constant 12v nor any brake output. On the Yukon XL the constant 12v is there as it should be per the label but it's what's causing the trailer brakes to be locked up (I verifed this by removing the pin internally in the connector but then I have no brakes). I really want to avoid switching pins around and I wanted to ask if anyone else has had a similar problem to this? Or maybe did I somehow blow up my brake controller? The Yukon XL does not have any blown fuses that I could find (I haven't checked the Yukon yet) and each vehicle behaves consisent (i.e. Yukon has zero trailer brakes all the time / Yukon XL has 100% trailer brakes all the time) regardless if the brake controller is plugged in or not.

Another question is am I correct to assume that brake controller don't send variable voltage to the trailer brakes but instead put a variable resistance against a constant 12v instead? (i.e. no resistance = 100% braking / Full resistance = no brakes)

Thanks to all who read this entire saga and actually respond as well...

Tage

[email protected]

Woodcutter · January 30, 2008

Tage, sorry to read about your dilemma. How old is your Tekonsha? It sounds like your brake contoller might have bitten the dust. Since your new Yukon XL has a plug-in pigtail harness, I would try to borrow someone else's brake controller to try and narrow down the possibilities of where your problem is (brake control, wiring, plugs, etc.)

Good luck.

pwall · January 30, 2008

I hope this isn't a stupid question but I didn't see it in your post. The YukonXL, is it new ?

My thought is if it is an older vechicle, the trailer connection at the back of the truck could easily be shorted out. This is common up North where road salt is used way too often.

Tage · January 30, 2008

The brake controller is just a few months old. The Yukon XL is a 2003 and an Arizona vehicle (i.e. no snow or salt) so the plug and connections look near new. I checked the functionality of each pin with my DMM and they appear to be working correctly per the description on the molded plastic cover.

I posted this on another forum and another owner brought up a good point that it could be my trailer brake away system manfunctioning causing it to lock up the brakes. He suspecting either the switch or low battery, etc. It's quite the conicidence that it worked fine just a few days before but it is possible and at this point I'm checking everything so that will be the next on my list.

My brake controller is fairly popular along my local racing/trailering buddy's so I'll try doing some brake controller swapping to see if I have a bad harness or controller too.

Just want to make sure I didn't miss something like, "the blown brake controller fuse hidden behind the ash tray or something"...

mljenkins · January 30, 2008

Not having a lot of time to read throughly, your brake pin and 12V constant pin may be reversed in your trailer wire harness. Some vehicle harnesses have these two switched. I bought a 7-way to 6/4-way converter and it has in the instructions how to take it apart and swap the pins for this situation. The fix would be very quick, just take apart the connector on the end of the trailer's umbilical and swap the 12V AUX and brake.

No brake is NOT a constant 12V, otherwise your brakes will lock every time your controller kicks in. I have the Prodigy brake controller and have never had an issue with it, and it really saves the truck and trailer brakes being a proportional controller. It has always been wonderful to detect shorts, disconnects, etc. between my two trailers I tow. If it is showing not connected, it means somewhere in the wiring it is not seeing your trailer brakes. If the pins are swapped in the harness, that would cause the issue.

Pinout for your truck should be on the cover to the trailer wire cap. Easiest way to find the pins on your trailer (if you take the harness off and forget to write the colors down to which pins or something dumb like I have done) then first find the ground pin, hook it to a 12V ground, and then start shorting the other pins to 12V positive and have someone watch the lights. When you find the brake it will spark when you touch it to positive as they pull a lot of juice + you will hear them hum as they get power. 12V AUX can be found by turning on the light inside your trailer (if you have one) or watching the brakeaway battery charge indicator light (if you have one).

Tage · January 30, 2008

Not having a lot of time to read throughly, your brake pin and 12V constant pin may be reversed in your trailer wire harness. Some vehicle harnesses have these two switched. I bought a 7-way to 6/4-way converter and it has in the instructions how to take it apart and swap the pins for this situation. The fix would be very quick, just take apart the connector on the end of the trailer's umbilical and swap the 12V AUX and brake.

No brake is NOT a constant 12V, otherwise your brakes will lock every time your controller kicks in. I have the Prodigy brake controller and have never had an issue with it, and it really saves the truck and trailer brakes being a proportional controller. It has always been wonderful to detect shorts, disconnects, etc. between my two trailers I tow. If it is showing not connected, it means somewhere in the wiring it is not seeing your trailer brakes. If the pins are swapped in the harness, that would cause the issue.

Pinout for your truck should be on the cover to the trailer wire cap. Easiest way to find the pins on your trailer (if you take the harness off and forget to write the colors down to which pins or something dumb like I have done) then first find the ground pin, hook it to a 12V ground, and then start shorting the other pins to 12V positive and have someone watch the lights. When you find the brake it will spark when you touch it to positive as they pull a lot of juice + you will hear them hum as they get power. 12V AUX can be found by turning on the light inside your trailer (if you have one) or watching the brakeaway battery charge indicator light (if you have one).

Good stuff man!

I did take apart my converter and saw where I could switch around the two pins but I wanted to avoid that since I felt like it would be a non-standard setup. I did disconnect the one that had voltage causing the 100% brakes so I could at least drive the trailer to the track and just said to hell with the trailer brakes and just drove cautiously. I'll give the pin out switch-a-roo a try as that will be the easiest one so far to try.

desrtrat · January 30, 2008

what year was your old tow vehicle? brake controller harness were changed in 03. a harness that plugs into the panel by your left foot for a 01-02 will not work on a 03+ i can't remember, but 2 wires need to be changed in the plug for it to work. just get a harness for the year of the truck, and you'll be good

Tage · January 31, 2008

Both vehicles were 2003 GMC's.

It was the converter. I did the 2 pin switch-a-roo and it works like a champ. I'm really kicking myself now because when I opened up the pin connector to disconnect the wire that was causing the brakes to be full lock I even said to myself, "I should just switch those two wires around to see what happens... nah". I even went so far as go to the parts store at midnight the evening before the track day and disected another plug converter and said, "yep, mine is wired right!".

That's just retarded that GMC switched the wiring around from 02 to 03 IMO...

At any rate, it's fixed and thank you SO MUCH for all the support guys! I have a bunch more questions but I'll make separate threads for them.

Woodcutter · January 31, 2008

Glad to hear you identified the problem. Good luck with your new tow rig!

mljenkins · January 31, 2008

Glad to hear you got things fixed up. Now I am interested how well your 6.0 pulls compared to the 5.3. I have a 5.3 now w/ 4.10s in a 1500, and am wondering what a 6.0 would help with my 6500 lb goose neck (not including horses). The hills really bog the 5.3 down.

Tage · January 31, 2008

This learning experience has given me a cool idea. I'm actually going to pick up another adaptor plug and keep it wired incorrectly and use it as an anti theft device for when I'm traveling. As a guy who's had a car stolen 3 different times and I'm constantly hearing of other racers getting their entire tow rig (truck, trailer and racecar) stolen, I'm a bit paranoid of theft. I've got an alarm on the Yukon (w/the siren INSIDE the cabin - since no one cares about alarms anymore anyway), a club on the steering wheel, a trailer boot/lock on the trailer wheel and then I'll have the wrong plug on the wiring harness. LOL!

I'm actually thinking about disconnecting the trailer and putting my tongue lock on the trailer as well. Then if someone wants to steel the trailer, they will have their work cut out for them to get all the locks off and then hook up the trailer before they can leave.

As far as the 5.3L vs the 6.0L. The 5.3 is weaksauce IMO. Both vehicles have 3.73 gears and I assume the Yukon XL is a few hundred pounds heavier but it's definitely a noticably more powerful motor. My wife doesn't pay much attention or really care about engine performance but she even commented that, "holy crap, this has WAY more power". While towing it gets up to speed noticably easier and I can actually drive the speed limit (i.e. 65mph) and maintain it w/o constant and annoying downshifts while towing.

On the flip side, it still is a gasoline engine which IMO suck for heavy towing applications. My trailer loaded runs in the 6000-7000# range and the fact that it's about as aerodynamic as a parachute makes for horrible gas mileage and makes me feel sorry for the engine when leaving from a dead stop or maintaining freeway speeds. If I try to baby the gas pedal, it simply takes too long to get moving at the pace of cars around me. However, if you compare the 5.3 vs the 6.0 it's "better" but far from "good" IMO. I really wanted a turbo diesel but the wife said no way in hell she's driving something that sounds like a semi truck. Since the Yukon is "her car" and "my tow vehicle" we had to compromise.

FYI - My buddy has a Dodge turbo diesel and we got 16.1MPG towing about 5500#'s of trailer/car from Phoenix, AZ to San Diego, CA (mostly flat but about 50-75 miles of hills/mountains) @75-85MPH!!! While towing it still had more power and acceleration than my daily driver (4 cylinder Honda Accord)! He said when driving closer to 55-60MPH he averages 20+MPG while towing.

In your situation, I'd say your 4.10 gears w/5.3L is probably a wash compared to a 6.0L w/3.73 gears. If you wanted to compare apples to apples, you'd need to upgrade the motor while keeping your lower rear end gears.

I'd say the bottom line is, for towing, bigger is better and diesel is best.

mljenkins · January 31, 2008

Sounds you have bad luck with theft in your area! Interesting idea on the trailer wiring mixup. Just watch because if you leave it connected 12V aux supplies power all the time to the trailer so you will run the truck battery down and maybe harm your trailer brakes. IMHO you may be better just padlocking the trailer to the truck using the safety chains to the receiver holes for the safety chain hooks. They would have to steal your truck at that point or cut the chains. If they stole my rig I could run after them and catch it, HAH! Feels like it sometimes.

The new Duramaxes I have heard are almost as quiet as the gas models. I would like a dmax but the price is just too high for me right now for the amount of towing I would do with it. Good to hear the 6.0 can perform better on the highway. I towed from WV to OH about 300 miles last summer with about 7700 lbs (trailer + horse + load) in the gooseneck with the 5.3 and was fine on the interstate. I towed north this year with my 4000 lb bumper pull trailer (coming back maybe 6000 lbs) to PA and it just kept downshifting. Point being the hills just kill the thing, and unless I go west from where I live I have to pull hills. I am anxiously awaiting to see if prices drop when the smaller dissel comes out in 2010, if it does.

Tage · January 31, 2008

Yeah Arizona has horrible theft rate, especially being close to the border. Some people just don't care. I had a friend get their BMW stolen out of their work parking lot. A tow truck came and acted like it was a repo or whatever and yanked the car up on a flatbed with the alarm going off and everything. My friend saw it and ran out to the parking lot and they took off before the car was even all the way on the flatbed (still got away with it though).

I'm pretty sure the voltage is applied to the brakes only when the key is on or truck is running so that shouldn't be a problem with battery drain. My goal for anti theft would be to make it as hard as possible to steal either and not both.

Locking the chains to the truck is actually a good idea, especially if I disconnect the tongue and then lock the tongue individually. To steal the trailer and race car only, the theft would have to remove the club, cut the chains and disable the alarm before they could move the truck out of the way. The alternative would be to yank the trailer tongue away from the truck but with the chains locked to the truck it would add a couple steps to the process.

If someone wants to steal it, it's not hard it just takes time. My goal is to make it take as long as possible...