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Old 05-01-2016, 07:02 PM   #1
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Breakaway switch install / direct short mystery.......

1966 Avion T-27 with tandem Dexter #3,500 axles, axles replaced by PO around 2012 with some "interesting" brake wiring approaches. Trailer was extensively refurbished in 2008 / 2009 by a competent shop.

Current item - Breakaway switch was inop. - may have been the entire time I have owned the trailer...................3+ years.

Everything else "appeared" and felt (brakes) to work fine. (Gain / brakes worked good set to 6.5/10 on Ford F-150 factory controller)

Went to wire in a new breakaway, while I was in there I noticed that the brake connections from the umbilical to the trailer wiring were shoddy (wire nuts and tape) so I wanted to redo those with watertight crimp connections. Also, there was some corrosion (blackened copper) in the white (ground) umbilical line which I cut back. There is also a shoddy ground tie in from the umbilical and brake line to the belly skin instead of to the frame. Need to address this as well.......pending.

Now here is where I am getting lost / confused.

The 2 wires (red sheathed pair) running back to the brakes are black and white. (Also disappears into the frame rail - more on that later)

(1) If I wired the blue from the umbilical to the black from the brakes, and the white from the umbilical to the white from the brakes - "No Trailer Connected" message from the factory installed. And yes, I don't remember how they were wired / color matched to begin with................

(2) If I wire the blue from the umbilical to the white from the brakes, and the white from the umbilical to the black from the brakes, "Trailer Connected" on controller and the brakes work.

But then, if I wire in the breakaway to the #2 configuration above with one side to the umbilical blue / trailer brake white and the other side to a hot lead from the fuse panel / battery (had a 30 amp auto reset breaker inline there to begin with) unhook the umbilical and pull the breakaway pin, I get an instant short that blows the main 50 amp blade fuse that is right at the battery positive feed.

FYI - I don't believe in an unprotected circuit - even for brakes.

I have replaced all the wire from the breakaway to the umbilical tie in and checked the continuity of the new breakaway switch. All OK.

So, what am I missing? Is that shoddy ground the main culprit?

More info for the bored / entertained - Brake wires at the axles - don't even ask - appears only the "hot" wire is used and the main ground wire from the front tie in to the umbilical is clipped off and capped. Main brake wires from the front must be spliced in the frame rail run somewhere (trailer has a riveted aluminum sheet underbelly like an Airstream) as the are 2 pairs of wires coming out of the frame rail at each streetside axle location. Then, 2 wires run thru each axle tubes to the curbside brakes. Grounds from the streetside brakes all tie to the frame. And, the wires exiting the frame rails are older and yellow and black.........?

Access to the umbilical tie in is via a small 6x6" or so panel on the belly up front. (while laying on gravel and cardboard!) Umbilical was replaced in 2009 or so. Also, over the POs and service, there is not much play left in the umbilical wires (cut a bit shorter every time someone "rewired" something).

YIKES!

If I can't figure this out I'm thinking of just getting a new umbilical and running new brake wires INSIDE the trailer and exiting near the streetside wheel wells. I don't want to drop the belly pans for this.........

Is it possible for the controller to be OK with a reversed wired brake system? But, the breakaway is not? (direct short to ground).

Anybody know of a good shop for such in the Central Texas area?

Top is "not in the business" anymore.

And, I'm not really supposed to be "working" on the trailer in the storage yard, and I can't at my house either...........HOA...don' go there!
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Old 05-01-2016, 09:57 PM   #2
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Were both the white and black wires from the brakes (red jacket) connected before? If you are not sure, try configuration #3, which is like configuration #2 but only connect the blue wire. A/S often used black for 12V hot lines. In my trailer black is also used for the backup lights.

If configuration #3 doesn't work, you're going to need a volt-ohm meter. HF sells one for about $7. Big box (HD, Lowes) also have them. With the umbilical wires disconnected from the brake wires, put the meter in DC volts and a scale that will read 12 volts. Have someone actuate the manual lever on the brake controller. Verify that 12 volts (at maximum lever position) shows up on the blue wire. If not check the white one. The one with the voltage is your brake line.

Again with the meter in 12 volt mode, measure from the black and white brake cable wire to the frame. You should not see any voltage. If you do, the wire with the voltage is not related to the brakes.

Assuming neither wire has voltage on it, put the meter in ohms on the lowest scale. Measure from the white brake cable wire to frame ground. Now measure from the black wire to frame ground. For a tandem axle trailer, the brake line should read around 1 ohm. This is because each magnet is about 4 ohms and they are all supposedly wired in parallel. If you see two ohms, only two magnets are connected. You should be able to connect the umbilical brake line to the axle brake line and the breakaway switch without a problem. If not your choices are to figure out the wiring (open up the belly pan) or rund new wires as you suggested.

At least that's my best guess.

Al
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Old 05-01-2016, 10:37 PM   #3
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Quote:
Originally Posted by Al and Missy View Post
Were both the white and black wires from the brakes (red jacket) connected before? Good question... If you are not sure, try configuration #3, which is like configuration #2 but only connect the blue wire. Will try...A/S often used black for 12V hot lines. In my trailer black is also used for the backup lights.

If configuration #3 doesn't work, you're going to need a volt-ohm meter. HF sells one for about $7. Big box (HD, Lowes) also have them. With the umbilical wires disconnected from the brake wires, put the meter in DC volts and a scale that will read 12 volts. Have someone actuate the manual lever on the brake controller. Verify that 12 volts (at maximum lever position) shows up on the blue wire. If not check the white one. The one with the voltage is your brake line. Verified - blue from umbilical has around 12 volts at max controller lever squeeze. White is zero.

Again with the meter in 12 volt mode, measure from the black and white brake cable wire to the frame. You should not see any voltage. If you do, the wire with the voltage is not related to the brakes. Verified - no voltage

Assuming neither wire has voltage on it, put the meter in ohms on the lowest scale. Measure from the white brake cable wire to frame ground. Now measure from the black wire to frame ground. For a tandem axle trailer, the brake line should read around 1 ohm. This is because each magnet is about 4 ohms and they are all supposedly wired in parallel. If you see two ohms, only two magnets are connected. Will give this a try. You should be able to connect the umbilical brake line to the axle brake line and the breakaway switch without a problem. I thought so to! If not your choices are to figure out the wiring (open up the belly pan) or rund new wires as you suggested.

At least that's my best guess.

Al
Thanks for the response and ideas.
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Old 05-02-2016, 09:39 AM   #4
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Here is what I might do if I was in your position....

I might run a new brake wire from the front of the trailer to the wheels under the trailer and start over.

With wiring, sometimes starting over is easier than trying to figure out what has been done.

That said, it might be possible that the dead short is in the break away switch itself.


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Old 05-03-2016, 12:13 AM   #5
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Regardless of the color codes, if the breaks work then you are halfway home.

Remember. The breakaway switch is supposed to apply 12 DC to the hot side of the brakes. In that way an auxiliary battery is locking the trailer brakes. This assumes the trailer has broken away from the TV, and the 7 way connector is broken loose as well.

If you tie the TV hot wire to the trailer brakes the 12 volt system in the TV sees the breakaway switch as a dead short and blows the fuse.

I would not wire the breakaway switch to the TV battery source. I would wire it to the hot side of the trailer battery and hope you never loose the trailer.

The hot 12 VDC supply from the TV is normally routed thru a massive diode to prevent the trailer charging system from frying the TV charging and regulator circuits.
Likewise, the trailer charger isolates the TV power source such that a dead trailer battery does not take down the TV battery.

The breakaway is a dead man switch, only to be used in emergency. Testing is destructive testing.

All the best, your mileage may vary, void where prohibited, object in mirror are closer than they appear, baby I won't.....you get the idea.

Happy Trails
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Old 05-03-2016, 09:01 AM   #6
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I would ground each wire at the wheels (after removing the supply voltage or unplugging the umbilical) and then apply a test lamp probe to each wire at the harness until I found the ground. Then do it for all the rest until I could identify the continuity of each unknown wire. The you can develop a circuit diagram.
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Old 05-05-2016, 04:21 PM   #7
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Quote:
Originally Posted by Jekerrville View Post
....

If you tie the TV hot wire to the trailer brakes the 12 volt system in the TV sees the breakaway switch as a dead short and blows the fuse.
....
Maybe, maybe not. Depends on the brake controller. If the TV brakes are applied, there is 12 volts on the blue wire with respect to both the TV and TT grounds which is exactly the same as what happens when the breakaway switch is activated. If the two vehicles do not have exactly the same voltage, then one battery will try to charge the other, but I doubt it would blow a 50A fuse. If, however the TV brake controller puts ground on the blue wire when the brakes are not applied, then the TT battery would see the TV brake controller as a low resistance to ground and might blow a 50A fuse. I suspect it would also blow the TV brake controller. I suspect, but do not know, that the break controller is an open curcuit when the brakes are not applied and there should be no problem pulling the breakaway cable with the TV connected. If the problem is the interconnection of the two vehicles and you should not pull the breakaway cable when connected to the TV , it can be easily verified by setting configuration 2 except leave the TT unplugged from the TV and then pull the breakaway cable. If the problem is the interconnection of the two vehicles then the fuse will not blow. IF the fuse does blow then you know the problem is on the TT.

I will say I have never done this on my setup. I have pulled the breakaway switch cable to test it and the emergency brakes, but not with my truck connected.

Quote:
Originally Posted by Jekerrville View Post
....

The breakaway is a dead man switch, only to be used in emergency. Testing is destructive testing.

...
Not my breakaway switch. Pulling it simply pulls an insulator from between two switch contacts which applies 12 volts from the TT battery to the brakes. You should not allow this to happen for very long, or the brake coils will overheat. They are not intended to have 12V applied for long periods of time. That's why there is a warning in the manual not to use the breakaway switch as a parking brake.
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Old 05-05-2016, 05:05 PM   #8
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Found this on another forum.....

Talking abut testing the breakaway switch.....

..."Don't try this with the trailer hooked to your tow vehicle, some have said it might damage your brake controller. I don't know if this is correct. Make sure the pin is completely seated, mine has an O-Ring to seal out the elements.

Two different brake controllers I own have said just that in the instructions. ..."

Your symptoms may be normal

Al
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Old 05-06-2016, 05:31 PM   #9
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Quote:
Originally Posted by Jekerrville View Post
Regardless of the color codes, if the breaks work then you are halfway home. I thought I was as well, but.....

Remember. The breakaway switch is supposed to apply 12 DC to the hot side of the brakes. In that way an auxiliary battery is locking the trailer brakes. This assumes the trailer has broken away from the TV, and the 7 way connector is broken loose as well.

If you tie the TV hot wire to the trailer brakes the 12 volt system in the TV sees the breakaway switch as a dead short and blows the fuse.
Did not do this or mention such....

I would not wire the breakaway switch to the TV battery source. I would wire it to the hot side of the trailer battery and hope you never loose the trailer. Agreed

The hot 12 VDC supply from the TV is normally routed thru a massive diode to prevent the trailer charging system from frying the TV charging and regulator circuits.
Likewise, the trailer charger isolates the TV power source such that a dead trailer battery does not take down the TV battery.
Not sure why all this is mentioned as I am NOT tying trailer brakes or breakaway to the TV hot.......... the hot from the fuse panel I mentioned is from the trailer fuse panel.

The breakaway is a dead man switch, only to be used in emergency. Testing is destructive testing. Um, should not be....

All the best, your mileage may vary, void where prohibited, object in mirror are closer than they appear, baby I won't.....you get the idea.

Happy Trails
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Old 05-06-2016, 05:38 PM   #10
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Quote:
Originally Posted by J. Morgan View Post
Here is what I might do if I was in your position....

I might run a new brake wire from the front of the trailer to the wheels under the trailer and start over.

Don't want to drop the belly pan / wrap - it is like an Airstream, aluminum sheet with about 4,287 rivets. I may run a new sheathed 2-pair brake line inside the trailer and exit it near the wheelwells - hope to not have to do this though.

With wiring, sometimes starting over is easier than trying to figure out what has been done. Agreed!

That said, it might be possible that the dead short is in the break away switch itself. Will retest the switch, but tested OK out of the package before I started.


Superat stultitia.

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Old 05-06-2016, 05:41 PM   #11
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I will revisit all of this tomorrow at the trailer.

Thanks all for the input
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Old 05-07-2016, 02:51 PM   #12
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Solved.............

The breakaway switch, when engaged (pin out), had an internal direct short via it's metal body to the chassis (ground). ZAP!

Brand new (have had for a year or so as a spare), out of the box Tekonsha Mod. #2009 "vintage" look all metal body and a brass pin...................

I initially checked switch operation for continuity in the wires with the pin out - tested fine - so I installed.

But with the pin out, it also has an internal direct short to the switch body which caused the direct short..........found that today.

Everything else tests out / works fine (#2 wiring version from initial post).

Lesson learned................though all the wire connections are all nice and tidy and I redid the ground to the trailer (frame instead of belly skin)

Guess I'll order the "plastic" body version switch.
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