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Old 11-14-2008, 10:36 AM   #1
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Tekonsha P3 giving me 'Brake output shorted' message

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Ok, the AS has been sitting for 4 months, it been washed, stripped, lazy polished, reclaulked and retrimmed. I finally got my 2002 Range Rover back from the mechanic (lost the head gasket) and dropped it off at AA-RV Parts in Portland, OR to get it wired to the brake controller.

I got the new Tekonsha P3 with the hope one day I'll just bury in the dash and not have ugly things hanging below the dash. When I got home, I tried it with the AS and it is giving an error of "Warning: Output Shorted". This cable and AS worked fine with my friend's GMC with a Prodigy controller 4 months ago for a 130 mile drive home and no issues at the time.

I took it back to AA-RV and they verified it was wired correctly and we plugged it into a 5th wheel in their lot and the P2 worked fine.

Back at home, after tracking all the wiring in the cable and figuring out it is correct, I'm now looking at the trailer itself. When I test from the common ground (big pin) to the brake line (10:30 o'clock position) I'm getting about 2 ohms. Considering that the electric brakes are basically an inductor that is an electro-manget... it should be a low resistance line to 12V DC and that value seems in the ballpark.

Does anyone know a typical resistance of electric brakes when measure from the front connectors... or is willing to measure theirs with an ohm-meter?

The wiring diagram for a 1965-1981 is:

http://www.airforums.com/forums/atta...9&d=1092149002
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Old 11-14-2008, 11:11 AM   #2
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Ron, I had that issue a month or so ago when we moved West with our trailer. Turned out one of the magnet wires had come unclipped from the actuator arm on the backing plate. It had dragged on the hub until the insulation wore through, and shorted. It's not a tough fix, the easiest way I know to isolate the short is to hook the tow vehicle up, and disconnect the brakes at the wheel, one at a time, until you stop getting the short message. That way, you'll know which one to take apart and look at.
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Old 11-14-2008, 02:17 PM   #3
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O63--

Terry... great idea and thanks. I'll try that but it may take a week to get the data... depending on the weather. It's Oregon afterall.
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Old 11-14-2008, 02:18 PM   #4
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O63--

Oops... forgot. Any idea what a reasonable resistance value is for the brakes?
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Old 11-14-2008, 08:50 PM   #5
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Mine measures 1.1 ohm blue wire at connector to ground. I have a dual axle, four brakes oval magnets.
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Old 11-14-2008, 09:19 PM   #6
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Roger--

Thanks! I have the dual axles but have not taken the brakes apart... yet. I just measured mine again and got 1.6 ohms so I'm puzzled why it giving me the warning. It probably just measuring current so I'll have to start dissambling to try and find the culprit like Terry suggested.

Airstreams are never simple.
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Old 11-17-2008, 04:48 PM   #7
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Ron,

Electric brakes are about 3 amps per brake. If you remember high school phsysics and "ohms law" it says "Voltage = Current x Resistance". If you solve for resistance by dividing both sides by current you get;

Resistance = Voltage / Current

Assuming 12 volts; Reistance for one electric brake would be about 12 volts/3 amps = 4 ohms per electric brake.

If you remember parallel resistance, then 4 electric brakes would be 4 resistors in parallel, or around one ohm to pull a total of 12 amps (3 amps per brake). SO it sounds like your 1.6 ohms is probably about right depending upon the brakes. But you must remember one thing, your ohm meter can't put out much current. If you do have a partial short somewhere, when "real voltage" is applied it may uncover the problem, meaning somehow intermittent, as someone else suggested.

Did you measure the resistance while moving the connector & trailer wires to see if perhaps you are getting a short based upon the orientation of the connected cable. That is easily done wtihout removing any wheels and such, and thus I would give that a quick try. Just connect your ohm meter and wiggle the cables and see if the resistance changes.

Hey, another possibility is that your trailer connector is wired wrong, and the guy whom had the trailer before you wired his vehicle in the same "wrong way". Not saying that is the case, but it is possible. For example, if blue wire was actually groudn on your trailer, you would also get the short indication. I only say this because 1.6 ohms does not sound way out of line unless there is some configuration on the brake controller for the "number of brakes" or something that would affect the "short detection" current threshold. (I don't think a prodigy does this though).

Good luck,
Don
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Old 11-17-2008, 05:40 PM   #8
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Ron, I just wet thru a similar problem with my 66 Safari. I tested, re-wired-retested and generally banged my head against the wall. Finally I took a real small file and cleaned all of the brass contacts on the trailer end plug. I then took a small flat blade screwdriver and placed it behind the brass contacts and GENTLY bent them forward, increasing contact pressure at the TV plug. Problem fixed and is still working great. Always try the easiest solution first. A bad connection at the plug will do really strange things to these controllers.

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Old 11-20-2008, 08:59 PM   #9
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C5Don--

Thanks for the all the data, I could not find the a typical value for brake current and that helps a bunch. I'm very familar with ohm's, norton's and watts in general so no issue their and thanks for point out the brakes are wired in parallel.

Alumanutz--

Yes, I tried wiggling the the connector and reverse engineered the wiring diagram of the cable and when I thought I had found the problem... I just realized that the wiring on the cable is the mirror image of the conntect on the trailer.

Not to mention it worked with my buddy's GMC prewired truck with a Prodigy controller. I'll clean all the connectors and hopefully get lucky.

I'll try and dig in to the issue on Sunday and get more data.
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Old 12-08-2008, 02:46 PM   #10
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All--

Over the weekend, I invited some friends over for dinner... on the condition that he brings his truck with the brake controller. It's a GMC and I was mistake since I found out it had a Tekonsha Voyager model. This was the same truck that we used to get the Airstream home.

Once we plugged it the GMC to the AS... everything worked as it should, no issues.

So now I'm trying to debug the P3. When I wiggle the cable into the connector in the back of the P3... I can get the following:

1. Brake output shorted
2. No trailer connected
3. Trailer connected and working... but the display seems to flicker

I called Tekonsha and got a person on the phone in a couple of mins. His name was Paul and he was very helpful . Paul gave me a tech bulletin to test the P3 and since he reminded me it has a lifetime warrently... and It's only 6 weeks old, just exchange if it fails the test.

For reference, Paul also said that the typical electric brake resistance is about 3.8 ohms per brake so he expected that my dual axles trailer should be about 1 ohm total resistance.

The plot thickens... and I'll try and get home and test it tonight.
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Old 12-12-2008, 12:09 PM   #11
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OK... I found the problem but it a bunch of small things.

I checked the connector in the back of the P3 and it seemed completely solid, no flex. So I started with looking at the cable between the TV and and AS. The cable connector that plugs into the airstream had a bit of oxidation so I fastened emery cloth around an old 1/8" drill bit and the cleaned up each socket.

With that the PC flickered less, but sometime would still say brake output shorted. So I then took the back off both connectors on the cable. The AS side looked fine, but their was some black corrosion on some of the wires on TV connector. I got a new Bargman 7 blade connector and cut 3" off the cable and installed it wire for wire.

With that, the P3 started working, no more error codes... but then I discovered that my left turn signal would not work on the trailer. The left turn blinky works fine with the Bargman diagnostic connector. It's always something.

Long story short, I pulled the wiring cover form the front inside of the trailer and tested both turn signals. When I tried the touble light, got a RT but no LT signal. So checked the wiring on the cable as well... no LT signal. Hmm... I then checked it with a DVM and could see the voltage varing on the LT. Hmmm so I check the LT blade on the TV connector... the one that the Bargman diag says works (it lights up the LED). No glow from the Test light... but with the DVM show varing voltage. What the heck?

Now I'm putting dusting off the EE hat... got voltage... but not enough current to run a wimply light bulb in a test light. OK... work upstream on the TV... and the trailer tow light controller. Hmmm... same thing... DVM show voltage but no light from the test light bulb. I pulled this module from a previous landrover that sold, but never tested since it had the round pin connector. My bad.

So I take apart the tow package module... and Land Rover's are just complex. This tow module has not just diodes... but MOSFET and digital ICs.

One of the FETs was obivous toast (literally) and I headed to local electroics store and manage to get their last replacement FET. Fixing it was pain since it had burned the traces on the board, and needed jumper wires to remake the connections... but it is now back in and the left turn now works.

Next time... I going to just go nuts and clean every connector, do visual check of the wiring and then test the TV with a test light and not the high tech Bargman diag connetor. That would have saved me lots time and frustration.

Live and learn.
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Old 05-06-2015, 07:30 AM   #12
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I know this is a seriously old thread, but I just have to say thanks to Overlander63 (post #2). We had this error on our brake controller as we hooked up to head home yesterday. We were stuck in Goose Point Campground on Philpott Lake (Virginia) with the "Warning, Output Shorted, No Brakes" error on our controller. Go to RV Park Reviews and read the comments about the road into this park. It has some scary 10-15% grades that work a fully functioning rig really hard. I was not going to risk that road without brakes. After an hour or so of testing everything on the truck and the trailer plugs we ran across this thread and took the advice of cutting the wires at the trailer brakes one at a time. I was wiring each one back up when the error did not clear. Finally, when I cut the line on the very last brake it cleared. I was able to leave that brake disconnected and the rest of them started functioning properly. This was enough to get us down off the mountain and get us home. In fact, it worked perfectly after that. I am new to RVing, but have been pulling boat trailers for years. Electric brakes are very different from the surge brakes on the boat trailers. The dealer was not able to help, but this forum sure made the difference between being stuck on a mountain or making it home safely. Thanks for the knowledge and discussion you guys share!
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