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Cant find power source!

lovemyhd

lovemyhd

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:mad2::mad2::mad2:
Trying to hook some rear utility lights in the back of my truck. Trying to hook them to the button on the dash for the "plow package".....the button right above the fog light button. This button also turns on the white lights next to my 3rd brake light. Pulled the dash apart and got to the plug. Tried with my test light and cant find power on any of these wires.....even when the lights are on next to the 3rd brake light. HELP!
I dont want to add another switch to my dash, i want the lights to work off this factory switch
 
I personally do not like test lights, as they won't protect the circuit like a multimeter will. Anyway, if you can, try to find a multimeter, and then find a good ground under the dash, and then probe each slot on the back of the connector when it is hooked up to the light button. That way, when you find 28vdc, you can verify if the light button turns the 28v on and off. That's where you can tap into it. Jerry.
 
But doesnt a 12V test light do the same thing? It works on all the fuses and such.
The wires coming out of the switch are also very small.......probably 20gauge or something similar
 
the button you speak of, is for the cargo light, and is not specific to the plow package. the button that comes with the plow package, is by the airbag shutoff. that has a relay (i believe) and the end point is in the roof, with wire nuts and tape. it is put there so that when guys have a plow on the truck, they can wire the amber rotator to that switch and wire, without having to run the wire from the rotator through a window and into the cig lighter.

sorry, just had to clarify
 
I found power to mine. Don't remember which wire but it works.

And the reason for the small gauge wire is it only runs the relay, so don't put too much load on it or you will fry it.
 
Everyone is correct on what they are saying. The switch you are speaking of is the cargo lamp switch. The aux lamp switch (if so equipped) is located to the right of the HVAC controls and will have a relay powered harness with blunt cut wires in the passenger B-Pillar. This wiring was intended for use as a roof beacon.

As for tapping into the cargolamp circuit to hook up your lamps. The switch itself most likely switches a ground circuit, not positive (as most switches in 99+ GM trucks switch low current ground). I dont' have the wiring diargams for your 05, but IIRC the cargolamp switch for my 02 switches a ground to the BCM, and the BCM controls the relay for the cargo light itself. The best way to wire additional lights up with this circuit is to use another relay that you add and have it trigger with either the ground signal from the cargolamp switch OR the hot wire going to the cargo light itself.

If you need some more help I can take a look at some wiring diagrams later and let you know which wire at the switch is the switched ground.
 
I had heard that it switches a ground......And your right.....after looknig further, it's the cargo light. Seems like the cargo light switch and the fog light switch are run off the one plug. I'd definitely love some more help installing this setup as I'd much rather use the cargo light switch than adding another switch to the dash.
 
You can still use the shunting voltage to ground switch. I have a similar setup with my trucks high idle switch. I flip the switch and the poliot light comes on(I like pilot lights to much.)

Do it backwards, have a constant positive going to the lights you want operating, and have the ground act as the switched conductor. Just don't mix up the wires!
 
My best suggestion is to figureout which wire is the switched ground (prefferably with a multimeter but you could use a testlamp if it's hooked up to 12v on the other end, then find the ground that switches with the cargo lamp switch). Once you find the switched wire, tap into it and connect it to terminal 85 of the relay. Connect terminals as follows.

30 - 12V constant battery power. (This feeds your accessory so use the appropriate sized wiring)
85 - coil switched ground (in your case the switched ground from the cargo switch)
86 = coil power 12V (this wire can be a small wire tapped from your other power source, it just has to power the relay coil, nothing more)
87 = 12V switched power output (run this wire to your lights)

Let me know if you have any other questions.
 
Man, that is a huge help.......thank you very much!!! I have to work all weekend, so I wont get to play with the truck til Mon or Tues....but I'll let you know how it goes.....thanks again
 
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