reverse light wire color

I am in the middle of fixing a install by worst buy and have a question. I need a 12+ reverse gear wire to trigger a display in the rear view mirror camera screen.Does anyone know what color this wire would be and a good place to access it? It is a 1997 cadillac deville base

     Reverse Lights          LIGHT GREEN          (+)          SWITCH ON TRANS.Let's Go Brandon Brown. Congratulations on your first Xfinity Series Win. LGBFJB

Plan B :- Test colour at rear light, follow it on loom and pick it up at which ever kick panel (probably driver's) it runs to. Just hope it doesn't do either a Peugeot or Winnie and change colour halfway through.

Have them do it. You paid for a service, and the installer probably did not test to make sure it was working before it left. They have a lifetime craftsmanship on their work. Be polite to explain the situation, and you shall usually receive better/immediate service. If not, then the installer should not be in the business. If you mess with it you void that warranty. Also if you hook it up to the wrong wire, you not only void your craftsmanship warranty, you also void your parts warranty as well if it causes damage to the unit. If you wish to do it yourself though: 1. apply e-brake 2. turn key forward to acc/ign position 3. hook your black probe on the multi-meter to a ground 4. Hook the red probe to the wire in question, move the gear shift into reverse, it should read 12v+ only when in reverse gear.