Trailer wiring help


  #1  
Old 04-06-19, 01:17 PM
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Trailer wiring help

V70 2004

I have separate amber, stop, and normal lights.
I'm having trouble finding the brake and normal lights in this circuit.
I found left and right turn as they pulse (green and green striped in the photo).
However, the yellow wire actually goes off when I press the brake pedal -was expecting the opposite.
tbh, the turn lights are the same - they have a signal when off, but when the light is flickering, the signal pulses. Should both have power even when the signal is not on?

The blue and black always seem to on even when I take the ignition key out.
Any ideas how to troubleshoot?
V70 trailer wiring https://imgur.com/gallery/ECyyZw2
 

Last edited by qwertyjjj; 04-06-19 at 01:36 PM.
  #2  
Old 04-06-19, 01:46 PM
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The link you posted doesnt work.
 
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Old 04-06-19, 02:13 PM
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Seems to work:
V70 trailer wiring https://imgur.com/gallery/ECyyZw2
 
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Old 04-06-19, 03:09 PM
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The link doesn't work for me either, but, from what you're describing, it sounds like a bad ground connection someplace.
 
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Old 04-06-19, 03:30 PM
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Along with your grounds, check your bulbs and sockets. Have you replaced any bulbs from the time that everything worked properly to now? A worn or corroded socket can cause similar problems, and it is possible to install come bulbs anyway into a worn or sloppy socket opposite of how they should be.
 
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Old 04-06-19, 03:45 PM
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Sorry I should have been clearer. Everything is working fine on the car.
When I press the brake, the light comes on.
wheni signal, the lights come on.
I am probing the wires to find which is the right one to connect to the trailer kit.
is it possible that a wire would signal off to make the light come on? Like it's allowing another source wire then power the light?
Car
https://imgur.com/gallery/sJReUzD

Maybe I should look for voltage or amps instead of just a connection sound?
by the way, my ground for this probe test is just connecting the black probe to the metal chassis of car. I'm probing the wires with the red probe.
 

Last edited by qwertyjjj; 04-06-19 at 05:21 PM.
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Old 04-07-19, 04:11 AM
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And how do I find the taillight wire if the wire always has power in it?
 
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Old 04-07-19, 04:27 AM
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Now that I can see your picture I finally figured out that you are not working on a trailer. You are trying to diagnose your vehicle wiring so you can install a trailer tow socket on your vehicle.
 
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Old 04-07-19, 04:57 AM
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In that case, have you checked to see if your vehicle might have a connector at the rear where you can simply plug a trailer harness inline? Tell us what vehicle you are working on and maybe someone can tell you what they did with it or a similar vehicle.
 
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Old 04-07-19, 05:07 AM
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There is a harness in the picture, those are the wires I'm probing because I have a custom splice kit not the OEM plug. This harness is where the OEM plug would connect to to then go directlydto the trailer. It's a Volvo v70 2004
 
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Old 04-07-19, 05:29 AM
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is it possible that a wire would signal off to make the light come on? Like it's allowing another source wire then power the light?
Yes. When you have two power wires you have no ground so it shuts off. One wire loses power that somehow gives it a ground and it comes on.

On my truck I have a sun visor with clearance lights and I wanted the outside ones to blink with the blinker. Guy on a Chevy forum drew it up for me, not positive on the explanation though - long time ago.
 
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Old 04-07-19, 05:51 AM
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Unfortunately there is no universal standard for trailer wiring colors.
The only way to be certain about what each wire does on your harness is to get a wiring schematic for your specific vehicle.
There will be a wire there that is constanly powered in case you have a trailer connector with more than 4 wires.
The way to determine what you have would be with a test light.
Connect the clip on the test light to a good ground on the vehicle then probe each wire with the tip of the test light and go through the different operations and mark the wires.
After you determine which wire you need use a multitester to figure out which wire on your harness is ground.
You need to first determine the correct wires before you determine which is ground on your harness.

My suggestion though would be to purchase a harness that is made to conect to your vehicle.
Once you plug in the harness with the correct trailer connector for your use you will be done.
 
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Old 04-07-19, 06:39 AM
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I have already tested. I found left, right, and brake.
the tail lights seem to be harder since I can't find any wire that goes off or on when the key is removed from ignition and lights go off.
each bulb seems too have a few wires to it's socket, maybe I could try those..
 
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Old 04-07-19, 07:31 AM
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You need to keep in mind that some vehicle wiring does not allow separating the wires to allow a traditional trailer lighting hook up.

This is what you need.
 
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Old 04-07-19, 07:38 AM
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I have a curt almost like that.
I'm planning on splicing just where this harness is in the picture. Still can't identify the taillight wires though.
 
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Old 04-07-19, 08:14 AM
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In my car I used a no connection trailer harness kit. It's about a hundred bucks but you do not touch the vehicle's wiring. You simply clamp the sensors over a wire leading to the light.
 
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Old 04-07-19, 08:17 AM
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OK......now I understand.
I have no direct experience with your vehicle model but there is another adapert that is more simple to install.
On some like yours you have to actually ground the brake light cct but I can not help with that.

Unless someone else can tell you for sure how to connect your vehicle this is what would help you.
What you have is a less expensive ver of this that makes you hack into the vehicle wiring to make it work.
 
  #18  
Old 04-07-19, 11:55 AM
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I used a voltmeter instead of connectivity ohms to check...
https://youtu.be/g9XSNq_sYhE
 
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Old 04-07-19, 03:45 PM
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Yes, you would use a voltmeter to determine which wires are L and R signal and Park but you need an ohm meter to figure out which wire is ground.
 
 

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