Hardwiring V1 from previous hardwire

[NYankee]

I have searched and can find no definitive answer. I just bought a car with a 5 volt cord from a previous detector. I was just going to cut off the end, and splice in a pre wired RJ connecter. Which side of the connector goes to positive, and which side goes to ground?

[speed-dreams]

just get the V1 hardwire kit and a fuse tap, and you will be set...

[SquiddOhio]

The red wire always goes to positive (hot) side, and the ground wire is usually black (that's the convention, but your previous owner may not have followed it).
If looking at a previous installation that you did not do, use a simple tester, or even rig up a 12v light to test the circuit. Hold the ground to a known ground (most bolt heads) and put the other wire to the unknown wiring. The side that makes the light go on is the red/hot/positive side.
You might get a little spark, but you really can't hurt yourself with 12v.
With electronics, you do not want to have the juice going in backwards, because you can never tell what that will do.

[kpatz]

Do you know what the previous detector was? If it was a Bel or Escort, it'll plug right in to the V1, though you'll lose the mute button functionality. If it's some other make, I'd just install a V1 hardwire kit. Then you can add a concealed display if you like.