No Power To Brake Line At Connector

duejo01 · April 3, 2011

Just got back from towing my trailer with no brakes for the weekend

Noticed my REESE controller was not sending a signal to the trailer even though all other connections to the trailer (signal, brake lights, clearance) were working. Assumed the controller was faulty, so bought a new one and replaced it (now is a PRODIGY P2).

One of the advantages of the P2 is that it tells me when it detects that I am hooked to the trailer. Plugged myself into the trailer, but controller continued to display "no connection". Asked someone else in the campground if I could try plugging into their trailer to determine whether the problem was with the truck or with my trailer. When I plugged into their trailer, the unit continued to display "no connection".

There is power to the brake control unit. There is power to the male connector on my truck EXCEPT to the BRAKE wire. I've checked all the fuses I can think of and I cannot determine if the BRAKE wire has its own fuse or where it might be. It certainly is NOT the brake controller; it's brand new and besides... it didn't work on someone else's trailer either.

Any clue where I can look for what seems to be a blown but unknown fuse somewhere?

duejo01 · April 4, 2011

So I'm thinking further about this problem. I tried pulling the 30 AMP fuse out of Stub 2 in the fuse box under the hood, and the entire brake controller went dead... which makes sense. But according to all I've read, that 30 AMP fuse is the one that sends the power to the dark blue brake control wire in the connector. Is it possible (does anyone think) that the fuse is actually faulty and is blown, even if the brake controller powers up when it's in place?

This is such a mystery since my brake controller has always worked fine up until this weekend....

duejo01 · April 4, 2011

This is turning into an ongoing journal of me trying to fix this, so for those of you that read this, you will at least have an idea of what I've all tried.

Today it occurred to me "I wonder if signals from the bus where the controller is plugged into is sending current to the brake controller? Specifically, I wonder if the "brake light" signal is being sent?

Took my voltmeter and checked the positive (good), ground (good), dark blue to connector (nothing really and that's the way it should have been), and red brake light feed. Brake light feed read zero without brake depressed (good), but with brake depressed and brake lights on, it read about 10V going to the unit.

So NOW the million dollar question. Is THAT my problem? Do brake controllers (remember, I started with a Reese when this problem started and am now using the Prodigy P2) require a voltage kick closer to 12V? Is 10V too low for it to determine its connected to a trailer and needs to send current to the brakes?

I will be searching and calling Tekonsha for an answer to that question... but maybe my problem is actually with the brake light sending unit....?

duejo01 · April 4, 2011

Digging deeper into Tekonsha's website led me to the statement that a power back feed on the brake blue wire would result in the condition I have been experiencing. Taking my volt meter to the connector at the back of the truck, I get a constant low volt (between .4 and .8) when the truck is powered up. When the truck is off (i.e. key removed, no lights on), reading is 0. When lights are on and truck is off.... .4 to .8. When lights are off, truck is off, and 4-way flashers on, I can watch the volt fluctuate in time to the flashers. In my books, this matches the condition Tekonsha indicates; a power back feed on the brake blue wire. Reese is a little more nebulous, but implies the same thing in their debugging guide.

The ONLY place this all comes together that would be an obvious fail point is the connector at the back of the truck itself. So, that's what I'm going to replace next. I've tried unplugging the wire cluster from the 7-plug receptacle and still measure the back feed... so the problem MUST be in that wire cluster assembly....

duejo01 · April 5, 2011

My ongoing saga... hope those who are reading this find it interesting.... I'm finding it frustrating!

Yesterday I thought I had pinpointed the location of the power bleed to the blade connector wire harness at the back of the truck. Since my local GM dealer wants $120 for a new wire harness and since this was a theory, I wasn't wild about spending that kind of money on an unproven theory. So I went back to the drawing board to try to figure out if there was some way to confirm the theory without dropping that $120.

It occurred to me to pull the harness out of the blades (easily done) and then trace the dark blue wire back far enough to get some slack. Now, if I CUT that blue wire, THEORETICALLY, that should isolate it from the harness (where I theorized the bleed was taking place) and the voltage should drop to 0 (my objective). Made sure there was enough slack, cut the wire, attached the voltmeter to what should now be a dead feed (no chance of bleed or crossover)..... and it still read voltage. *SIGH* So I've soldered it all together again and am exactly where I started.

My final theory after talking to the GM deal is that one of the million relays in the truck is faulty. Could be signal, could be brake, could be headlights. Who knows? Why in heaven's name GM would bundle it so that it comes anywhere near the dark blue trailer brake wire is beyond me, but it makes sense in a perverted way, I supposed.

I'm now left with no other option than to take it to a shop for diagnosis and repair. I cringe because I suspect this is going to be a pricey diagnosis and then a simple and easy repair i.e. replace a relay. But unless I want to run my own isolated feed from the brake control unit in the cab to the trailer and bypass the builtin wiring GM provides, I see no other alternative.

06_GMC · April 6, 2011

Wow sorry to hear man but sometimes just running a single wire is easier than forking over a couple Benjamins to some dude.

duejo01 · April 6, 2011

I don't give up THAT quickly! I'd LIKE to stay with factory wiring since it prevents having to mickey-mouse a solution!

The LAST experiment I want to try before taking it to a shop is to yank the turn signal relay out and then test the truck circuit. Note that I'm referring to the relay, not the flasher unit. I've read plenty of descriptions of where it's hiding but haven't found it yet.... above cab fuse box, left side, mounted against dash, black square/rectangle shape. Blade plug-in. (GM dealer kindly showed me what it looks like when I was there). I tried yesterday but gave up... it's pretty cramped under there!

My THEORY is that, if it's the flasher relay (which was ONE of the suspicions of the GM dealer), then when I yank the relay out and power up, the power back feed should be gone from the brake line circuit. If that proves to occur, then I will take the relay to the GM dealer and see if they can bench test it. The downside is if they don't bench test equipment or don't have the ability to bench test, they will likely want to sell me a new relay... and I already know THAT part costs about $80.... which again will be pretty steep for a theory!

BTW...note that these are Canadian prices and, as per usual, we pay outrageous amounts for parts....

Finally, since this has turned into a rather long chain, let me recap for those that haven't been able to follow what the problem actually is!

First of all, the title is wrong by me complaining about no power to the brake line at the connector. That is the dark blue trailer brake wire on your connector and it SHOULD read no power (0 volts) when the brakes are not applied. Power up on that line should only occur when the brake is depressed and your brake control unit sends power through it so that your trailer brakes are activated.

My problem is that there is a power leak into that circuit from somewhere when the brakes are not being applied. If the wiring were "crude", it wouldn't be possible because the feed would be isolated. But since this is an integrated circuit/option sold by GM "for convenience", the wiring disappears into the chassis abyss to re-emerge at the back of the truck at the connector.

Brake controllers interpret power in the brake wire feed as "the trailer is not connected" and so... won't do anything, leaving you with no brakes on your trailer when you're towing.

Note that I have been towing for about 20 years and this is the first time I've had this problem. For that matter, I've been towing with this particular truck for almost 5 years and it has always worked fine. This is a new development and obviously a failure has occurred in the system somewhere as opposed to a "wiring problem" that I might have done.

After eliminating virtually every reasonable explanation, I'm left with failing components as a factor and relays are the most common point of failure.

And that's where I am!

duejo01 · April 7, 2011

THE FINAL CHAPTER! YES, it's fixed!!!!

So after faffing around with the relay, I decided "you know... that advice was good.... why don't I just run a new wire from the brake controller to the back of the truck and be done with it?... and while I'm at it, I'm going to put a 40 AMP plug in that Stub #1 so that I have power to the back too.....".

Ran a test wire from the controller to the back of the truck, hooked it up to the trailer, and BINGO! Brakes activate correctly. OK. So I know that WILL work.

Found a good place behind the fuse box to thread the new wire through, thread the new wire down under the chassis, thread the new wire along the frame, up over the gas tank, down to the connector.... OK... now back to the front and tape/zip tie everything down so everything is secure.

As I'm working along the frame, zip-tying to the existing cable, I suddenly notice "HEY! The cable is split here... and look! All these wires are exposed!! And LOOK! Someone has stripped all the insulation off the red wire in the bundle!! And LOOK LOOK! The dark blue wire (code for the trailer brake wire) is completely separated!!!!!!!!" So there it was! The owner before me likely was trying to get his trailer positive connection hot (which is what the 40 AM in Stub #1 will do and was what I was going to do) and was trying to figure out why it wasn't... and ultimately just gave up leaving the wire exposed and the bundle open to the elements. Had I not discovered the exposed copper in the red wire BEFORE I inserted the 40AMP fuse, it likely would have blown right away OR very shortly after I started trying to use it!

So in the end, I COULD have just repaired the blue wire in the exposed bundle! But at least I now I know 100% that I have a clear and dedicated line from my brake controller to my trailer brakes!