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Old 12-07-2019, 12:39 AM   #1
scottz
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M.O.C. #19755
Blue Wire

I just finished cleaning up all the wiring in my battery compartment. I have identified all wiring except for one; a 16ga blue wire coming from the belly. Keystone must have thought it was important, they had it connected directly to 12V; not going through a breaker. I thought it was the CO detector, but it's not. With it disconnected, I can't find anything that does not work.

Any ideas?
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Old 12-07-2019, 07:33 AM   #2
masterdrago
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I've had the same question about that blue wire since Oct 2017and like you have no idea where it is connected. AND NOT FUSED AT THE SUPPLY SIDE. Not knowing what it is connected to makes me unsure about what fuse size to put inline. My suspicion is it goes to the charging sensing circuit of the converter but I've got a huge red wire (marked with blue arrow) going directly from the battery under the floor and most likely to the converter through the switch in the convenience center. Sometime later this weekend I'll get all this sorted out. I'll amp-probe the blue wire when I fire up power again.


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Old 12-07-2019, 07:56 AM   #3
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Just looked inside the converter and no blue wire. There is a blk - wht heavy pair from the bottom (converter positive + and converter negative -) going to the circuit board which also has no blue wires. I'm thinking the only converter connection to the battery is the one heavy red wire to Battery pos + connection. See diagram


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Old 12-07-2019, 08:13 AM   #4
Daryles
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Here is a Keystone color code chart. Hope this helps
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Old 12-07-2019, 08:35 AM   #5
akoske
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Your blue wire probably goes to the brakes break away switch
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Old 12-07-2019, 09:42 AM   #6
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Quote:
Originally Posted by akoske View Post
Your blue wire probably goes to the brakes break away switch
Thanks. That will be easy to test. And most likely not a great ides to fuse it but I'll see after checking the current draw when pulled but just for a short time. So Scott can pull the breakaway switch pin while the wire is disconnected and brakes should not react.
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Old 12-07-2019, 10:49 AM   #7
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Quote:
Originally Posted by akoske View Post
Your blue wire probably goes to the brakes break away switch
That is an idea. I'll check it this morning.
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Old 12-07-2019, 10:59 AM   #8
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M.O.C. #19755
Assuming your unit is wired like mine (might be a questionable assumption) here is where the other wires go:

#4 red - Converter
vio - Bedroom Slide control
wht - Tank heaters
red with a 20A in line fuse - Cord reel
red - Level Up system
red - 12VDC from truck
(several red wires, you just have to figure them out)
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Old 12-07-2019, 12:31 PM   #9
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M.O.C. #19755
Quote:
Originally Posted by akoske View Post
Your blue wire probably goes to the brakes break away switch
Confirmed. It is 12VDC for the brake break-away switch.

Thanks!
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Old 12-07-2019, 02:41 PM   #10
ChuckS
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Iím quite surprised that blue DC power wire for emergency brakes is not fused with a resettable breaker.. it sure should be
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Old 12-07-2019, 03:48 PM   #11
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Quote:
Originally Posted by ChuckS View Post
Iím quite surprised that blue DC power wire for emergency brakes is not fused with a resettable breaker.. it sure should be
That would be interesting to watch
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Old 12-07-2019, 06:02 PM   #12
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M.O.C. #19755
I'd rather have mine hot. What fooled me is that the wire goes into the belly; probably doubles back to the harness going to the pin box.
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Old 12-08-2019, 01:09 AM   #13
rohrmann
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If your breakaway switch had to operate in an emergency, who cares if the wire is fused, you want that sucker to work fully to stop that trailer, even if it comes to burning up the wire, so it should not be fused with a fuse or breaker.
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Old 12-08-2019, 08:03 AM   #14
scottz
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Quote:
Originally Posted by rohrmann View Post
If your breakaway switch had to operate in an emergency, who cares if the wire is fused, you want that sucker to work fully to stop that trailer, even if it comes to burning up the wire, so it should not be fused with a fuse or breaker.
And if it was fused, how would know if the fuse had blown, leaving you without emergency brakes? What if it blows one hour into an eight hour drive?

Perhaps I should, but I do not test my break-away every time I move.
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Old 12-08-2019, 08:20 AM   #15
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M.O.C. #20949
Fixed value fuse versus resettable breaker are entirely different applications. The emergency brake circuit should have a resettable breaker in the circuit to prevent catastrophic meltdown of the wire harness and brake magnets...

An appropriate sized resettable breaker will allow emergency brakes to do their job. If the brake circuit is activated due to break away plug being pulled out via cable itís not gonna take all day to stop the RV...

And if unit is stored away from home and some jerk pulls that cable and you have batteries installed at the least you can expect damaged brake magnets and over heated wire harness...

My unit has a resettable breaker... as it should have

YMMV
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Old 12-08-2019, 09:01 AM   #16
jeffba
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No mention of a resettable fuse

have not been able to find what I would call a manufacturers drawing either way though
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Old 12-08-2019, 09:29 AM   #17
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A manual reset breaker on the breakaway circuit presents the same problem as a fuse. No way to know if it has tripped without looking at it or testing it.

An auto reset breaker, in an overload condition, would repeatedly trip and reset every few seconds over and over as long as the overload exist, possibly eventually melting the wire.

An unprotected circuit also presents a problem. An overload condition would be continuous and could melt the wire.

No matter the configuration, you will never know if the breakaway will work without testing it.
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Old 12-08-2019, 12:47 PM   #18
ChuckS
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Itís easy enough to calculate the ďtotalĒ amperage draw on the brake circuit or simply use add Dexter service manual and they have a nice chart showing total current draw of 4 electric brakes... 10 amps with all 4 brakes applied at full power.

Pic is a typical wire diagram of trailer with emergency brake circuit fused..

Second pic from Dexters service manual

A 15 amp standard ATC fuse or resettable breaker would assure enough headroom for voltage drop along the length of the wires and the fact all four brakes are wired in parallel.

And part of my hook up routine is for wife to pull emergency brake key while I listen back at the axles for the ďtell taleĒ clunk indicating my emergency brakes do in fact work.

They are fused and I donít have to worry about burning up the RV with a pulled emergency brake key drawing full DC current until it melts the wire harness and arcs to something else
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Old 12-15-2019, 02:24 PM   #19
kdeiss
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No fuse or breaker gets my Vote one less thing to malfunction
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Old 12-15-2019, 02:25 PM   #20
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Service manual

ChuckS: where were you able to obtain a service manual?
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