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Old 01-14-2014, 11:57 AM   #1
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Trailer Brake Wiring Question

I have a 38' 2004 Alfa See Ya on the Freightliner chassis and I was looking for information about wiring up trailer brakes. It has the 7 way rv plug at the back of the coach and the blue wire for trailer brakes. I'm wondering if there is a plug or something like the newer trucks use at the fuse block make wiring this up easier. I know Tekonsha makes a wireless controller for around $300, but if I can save $200 by using a normal wired one that's money that could be used somewhere else. I will be wiring it up myself, I'm a big diy'er and automotive wiring does not scare me at all.

I appreciate your help and insight!
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Old 01-14-2014, 01:08 PM   #2
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I doubt you will find the connector installed on any freightliner chassis. The assumption is you will be towing a car and the break systems on them are varied and mostly not electric.

The P3 controller only has four wires, +12 VDC, Ground, Break Switch, and the famous blue wire to apply the brakes. This is not a very hard job at all. Here is the wiring diagram for the P3 controller.

Probably the simplest way to wire the brake switch is to add a relay to the brake lights. This relay is the one to use Amazon.com: Car Auto Truck Relay & Socket SPDT 12V 12 Volt DC 40A AMP 5Pin: Car Electronics

Pins 85,86 are the coil. Wire one to ground and the other to the break light wire. Pins 30,87 are the Normally open contacts. Wire one to ground and the other to the P3 brake input. This serves as an inverter and applies ground to the P3 when the brakes are applied.



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Old 01-14-2014, 01:29 PM   #3
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Take a look at this thread. There is wiring for a brake controller installed, you just need to wire it to the controller you are installing. http://www.irv2.com/forums/f26/brake...er-183232.html
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Old 01-14-2014, 03:56 PM   #4
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Thanks for the input guys, I appreciate it. I'll be towing a 24' enclosed car hauler. Theberry's, I like the relay idea and I wil definately look for the connector mentioned in the link that UsualSuspect posted. I was hoping to make this work without running 38' of wire or digging into the factory wiring harnesses too much.
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Old 01-14-2014, 04:18 PM   #5
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Quote:
Originally Posted by 1982 SS View Post

I have a 38' 2004 Alfa See Ya on the Freightliner chassis and I was looking for information about wiring up trailer brakes. It has the 7 way rv plug at the back of the coach and the blue wire for trailer brakes. I'm wondering if there is a plug or something like the newer trucks use at the fuse block make wiring this up easier. I know Tekonsha makes a wireless controller for around $300, but if I can save $200 by using a normal wired one that's money that could be used somewhere else. I will be wiring it up myself, I'm a big diy'er and automotive wiring does not scare me at all.

I appreciate your help and insight!
Find the other end of the BLUE wire and you have solved your problem. it should terminate someplace near the drivers area.

If needed buy a wire tracer at Harbor Freight that sends out a signal through the BLUE wire. Then using the sensor to trace where that wire may terminate.

Dr4Film ----- Richard
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Old 01-14-2014, 04:41 PM   #6
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I think I got the polarity wrong on the brake wire. It needs +12 VDC instead of ground but needs to be connected to the cold side of the brake switch. In that case pin 30 or 87 needs to be connected to +12VDC. In either case the relay is still a good idea to protect the P3.

Dick
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Old 01-15-2014, 06:13 AM   #7
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Quote:
Originally Posted by Dr4Film View Post
Find the other end of the BLUE wire and you have solved your problem. it should terminate someplace near the drivers area.

If needed buy a wire tracer at Harbor Freight that sends out a signal through the BLUE wire. Then using the sensor to trace where that wire may terminate.

Dr4Film ----- Richard
I agree. I lifted up the dash and on a quick look noticed several blue wires in the harness at various points, I'll have to find the right one.

Quote:
Originally Posted by Theberrys View Post
I think I got the polarity wrong on the brake wire. It needs +12 VDC instead of ground but needs to be connected to the cold side of the brake switch. In that case pin 30 or 87 needs to be connected to +12VDC. In either case the relay is still a good idea to protect the P3.

Dick
I understood your point, but thank you for clarifying. I've used switching relays and most systems on my race car I've wired up with relays.
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Old 01-15-2014, 06:41 PM   #8
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Quote:
Originally Posted by 1982 SS View Post
I have a 38' 2004 Alfa See Ya on the Freightliner chassis and I was looking for information about wiring up trailer brakes. It has the 7 way rv plug at the back of the coach and the blue wire for trailer brakes. I'm wondering if there is a plug or something like the newer trucks use at the fuse block make wiring this up easier. I know Tekonsha makes a wireless controller for around $300, but if I can save $200 by using a normal wired one that's money that could be used somewhere else. I will be wiring it up myself, I'm a big diy'er and automotive wiring does not scare me at all.

I appreciate your help and insight!
I have a 2004 Journey on a Freightliner chassis and did find the wires under the dash and hooked up a Prodigy brake controller. I tried but am not successful in attaching a photo of the wires. If you send me a PM or an email bobgilson at frontiernet.net I'll send you the a photo of the wires I found under the dash.
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