He ran a wire from an accessory on the fuse box which went to the switch on dash and a wire from the switch went to the tail lights and was attached to the green wire in the harness. The harness under the driver sill plate was butchered and had things going off it to different places causing the parking light and brake lights not to work. You already helped me with that mess last year. I ended up replacing the harness and finding a stray wire ground to the floor pan for some reason and thats why the lights didnt work. I do have a test light.
Dude, you are so close.
Ok, he ran a wire from the fuse box to the switch on the dash and then another wire from the switch to the reverse lights. Right? That's exactly what you need to do as well. Except, in your case, you'll be mounting the switch on the shifter instead of the dash.
Sounds like you are pretty familiar with what wires are or were used for the reverse lights by him. You said that you replaced the wire harness that goes under the driver side sill. So the green wire in that harness should be good from where ever it plugs into the main harness up front all the way back to the reverse lights. To verify that the green wire in your new harness is connected to the reverse lights, you could take a piece of wire and connect it to a 12v source and touch it to that green wire. You can use a fuse in the fuse box that lights up with your test light as a 12v source or the pos battery post. If the green wire is intact/connected to the reverse lights, they should come on.
Once you get this taken care of, all you have to do if choose a 12v source to use permanently. If you can find the pink wire that was originally used, that would be perfect. If you find the pink wire, hook up your test light to the wire and the other end on ground/chassis and turn the key on. The test light should come on.
If you can't find the pink wire or you find it and it doesn't have 12v with the key on, you can simply insert a wire under the glass fuse at the back up light fuse. We just need to be sure you put the wire under the correct end of the fuse. Basically, find the back up light fuse, pull the fuse out, ground your test light and with the key on, touch the test light probe to each contact of the back up fuse holder. One set of contacts should have 12v and the other should NOT. You want to put the new "pink" wire under the side that does NOT have 12v.
You will connect the other end of this new "pink" wire to one side of the switch at the shifter. Then connect the green wire to the other contact on the switch.
Hope this gets you there.
Post back if you need clarification on anything.