Trying to find reverse light wire and ground wire for reverse camera setup

Hey all, wondering if anyone has experience with this and can help me figure it out. Installing a reverse camera to my 2013 gu patrol. The camera needs to be connected to the reverse light positive wire, and then an additional connection to ground it.

Looking at the wiring looms and checking online, I can't find a clear answer as to which wire I should be tapping into:

Attachment 88700
Attachment 88702

Some pictures of the wiring I'm dealing with. Any help with identifying the correct wires will be much appreciated!

Thanks

Looks like you already have some additional wiring - trailer plug perhaps? Do you have a GU manual? You can download a copy from this site, or head to Supercheap and buy a Haines/Gregory or similar. Last resort would be to pop the tail light out and work it out from the bulb.

I believe the reverse light is the yellow one, but you should check with a multimeter between yellow and ground. Should read 0v in any gear and 12v in reverse.
For ground you can use any bolt that goes through the sheet metal.

Attachment 88704

Thanks for that, I tested yellow with a multimeter and it was only active in reverse, so you were right. The camera I'm wiring has a ground wire too that needs to connect to the "negative of lamp or chassis", and I'm unsure how to find the negative too. Some forums say black, but there's no black wire in the looms my patrol has by the tail light. Do I just use the multimeter to test each wire to find the ground? And what voltage would it be showing?

Thanks again

Mount the earth off anywhere on the body, doesnt need to be 'in the loom'.

Just like PeBee said, there is no need to go to the loom. If you check the diagram above, (Y)ellow brings positive to the lamp, and (B)lack brings ground. It is actually grounded somewhere near the lamp to save wiring. So any bolt that goes through the sheet metal is good. If you find one that already has other ground wires connected, even better.