If you want to add a backup camera to your 1999-2003 Grand Vitara or XL7, you can tie into this reverse light wire under the dash, right below the fuse block.
It’s red wire with two silver dashes.
While you’re at it, might as well and get a diode so you can put your reverse camera on a switch. I went with this Hopkins 48955 Towed Vehicle Diodes Kit.