double ground?

last year i wired a bullet camera in my car (12v 80mA) using the external power supply (4 AA batteries). now i'm trying to hard-wire it in and have it fused/switched inside the cab. the power is supplied via what i would call a stereo mini plug, such that when i cut the female end i had a red wire, a black wire, and a bare wire. i can test for continuity across the 3 sections of the mini plug and i have power at the tip, but for some reason the camera isn't working (and it works when i revert back to the external power supply). i'm guessing it has something to do w/ grounding and/or the bare wire. i have both the black wire and the bare wire grounded to the same spot inside the cab-- but now i'm wondering if this bare wire should be grounded some other way (since it is isolated from the other ground at the plug side after all). ?? any advice appreciated! thanks in advance.

I believe the bare wire is just to prevent interference.itmdtr

can you check the power output from the original hookup (do you get power from the red and bare, or red and black) usually braid is going to be just a shield, but it should power up, are you sure you have the right voltage?

well now i'm more confused... i did check the original (external) supply. it turns out that both the tip and the middle section are hot, and the base of the shaft is ground. so i guess that means the bare wire is also power ?? note: this is not shielding (at least like the braided kind i've seen), rather it is a separate 3rd wire (non-insulated) alongside the red and black wires (all 3 are then insulated). the other thing which confused me a bit (being a newbie to this kind of thing): the power from the external supply (4 AA batteries) was actually ~24 volts according to my multimeter. that said, the "output" rating of the optional AC adapter states that it is 12v. so should i try to make the bare wire hot in addition to the red wire (obviously now that it is stripped i'll have to wrap it up in electrical tape first)? maybe just splice into the red wire? does this make sense to anybody? (again, this is using a stereo mini plug) thanks!

sounds like it's a tip ring sleve connection.  i know in some respects the tip and ring are used for information, where tip sends and ring recieves and the sleve is a ground reference.... but that was in studio use.... i'm not sure how your unit is set up.... .just thought i'd throw that out there

4 AA batteries only comes to 6 volts. maybe the red and black are reversed. on a most 12v systems it really matters which is positive and negative.