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Old 02-06-2019, 08:50 AM   #1
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Trailer brake controller and wiring connection

Hey guys. I have a trailer that I like to tow with and it has electric brakes. The freightliner people I talked to said itís no problem using an electric brake controller with air brakes. Tekonsha P3 is by far the consensus best one out there.

My question is ..... where the heck are the wires under the dash to connect the brake controller? Are they just wires or do they actually have a plug head? Iíve looked around a bit under the dash and canít find them. Anyone located theirs and could provide some assistance? 2019 34QS
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Old 02-06-2019, 10:44 AM   #2
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ok ........ so digging around online there's lots of mis-information about the colors of the wires under the dash and how many of them exist.

on my rv under the dash, behind the pedals, there's a square divider piece with carpet on it. I removed that and I found the harness. The harness is a plug head with 6 wires. There is a label on the conduit that says "trailer brake controller" -- Just for reference, if anyone needs this info for their RV

I purchased the Tekonsha P3 trailer brake controller from amazon for $119. And theres a freightliner specific wiring adaptor they sell as well. The part number for the wire harness is 3027-P. This harness plugs into the back of the Tekonsha controller and the other end goes to the plug on the chassis for the RV. Plug & play. Should work perfectly.

I'll post back up once I recieve the items and install them. Ill do a video install if anyone cares to watch. I saw nothing online for this and it took me a while to find out all of this. So if I can post a video and help people on here in the future, Im happy to do it. Stay tuned. That's all the info I have so far.
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Old 02-06-2019, 10:46 AM   #3
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Quote:
Originally Posted by eagle5 View Post
ok ........ So digging around online there's lots of mis-information about the colors of the wires under the dash and how many of them exist.



On my rv under the dash, behind the pedals, there's a square divider piece with carpet on it. I removed that and i found the harness. The harness is a plug head with 6 wires. There is a label on the conduit that says "trailer brake controller" -- just for reference, if anyone needs this info for their rv



i purchased the tekonsha p3 trailer brake controller from amazon for $119. And theres a freightliner specific wiring adaptor they sell as well. The part number for the wire harness is 3027-p. This harness plugs into the back of the tekonsha controller and the other end goes to the plug on the chassis for the rv. Plug & play. Should work perfectly.



I'll post back up once i recieve the items and install them. Ill do a video install if anyone cares to watch. I saw nothing online for this and it took me a while to find out all of this. So if i can post a video and help people on here in the future, im happy to do it. Stay tuned. That's all the info i have so far.


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Old 02-06-2019, 11:23 AM   #4
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I did this and I just discovered I failed to do a writeup on it on my blog... sorry.

Two things.....

One: You may find the diagram below helpful.

Secondly.... Don't know if you have the same pigtail I got, but the power that goes to the trailer brake controller is the actual power activating the brakes. The wire dedicated to that in my pigtail had a fuse in it..... .5A and it was a very thin wire. So, needless to say the fuse blew the first time I hit the brakes, and after realizing what was going on it was clear that the very thin wire was insufficient to carry that current.

So, I bypassed the pigtail with the power from the coach to the trailer brakes with a straight piece of wire.
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Old 02-06-2019, 11:40 AM   #5
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Trailer brake controller and wiring connection

Quote:
Originally Posted by Oscarvan View Post
I did this and I just discovered I failed to do a writeup on it

Does your wiring on your RV look the same as mine with the same color wires and the plug head, etc?
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Old 02-06-2019, 12:37 PM   #6
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My wiring was the same as the diagram....From what I can see in your picture it is the same or very similar.

I don't have a picture that shows my wires.

After digging I realize the reason I don't have a writeup is because I ordered a one sided (the wrong) pig tail. IE, I had to do some splicing.

The correct one is indeed the 3027-P.

You should be plug and play good to go.
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Old 02-06-2019, 01:01 PM   #7
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These are the items I purchased, in case anyone wants to see what they look like.

There are 6 wires on the harness on the RV chassis (at least on mine, double check yours). These are the colors ....

Red (solid) - battery/juice/power
Red (w/white tracer) - output
Red (w/white tracer) - input to controller
Brown - backlighting
Black - ground
Pink - ignition

Since there are 2 red wires that both have a white tracer stripe on them, you'll need to figure out which is which. So just put a test light on each. Hit the brakes, and which ever lights up, THATS your power input to the brake controller. And of course the other red w/white stripe is your output telling the controller to let go.

The pigtail harness pictured below only has 4 wires. Since I have not received it yet, Im not sure which 4 they are. My guess would be that it corresponds to the 3 reds, and the black. Those are really the only wires that matter. So Ill report back once I get the harness and match everything up.
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