Display not working after replacing inverter, inverter cable + screen

I realize others have had similar issues and I have indeed read those posts but I have not been able to suss out what the issue is on my MacBook. I have the A1181 black MacBook 2,1 (2.16 Ghz processor). It's been a very solid machine and I've repaired it in the past (new fan, thanks iFixit!) as well as gone through several hard drives until I arrived at the SSD that's currently in it.

A couple of weeks ago when I woke the computer from sleep I noticed the screen was dark. I could still make out my wallpaper and icons on it. A restart seemed to fix the issue briefly before the screen went dark again. As with other people, if I lowered the brightness all the way down and brought it back up, the screen would work. For a few hours, the display stayed on at this lower setting. The following day though the screen would barely stay on for a few seconds using the same trick. Not knowing which component might have gone bad, I went in probably the wrong direction and did the hardest repair first: the screen itself. Got a used screen off eBay from a reputable seller. After going through the complicated repair, the result was the same. The screen is still dark and won't respond to the brightness button at all. When I connected the computer to a second display, that worked just fine. So I then replaced the inverter (A grade, purchased on iFixit). That changed nothing. So finally, I replaced the inverter cable (brand new on Amazon). That is also now not working. I actually put the old inverter back in with the new inverter cable and the screen or inverter seemed to make a strange light hissing sound. That made me wonder whether I'd somehow fried the new screen.

I suppose my next step is to put the old screen back in with the new inverter and inverter cable. Sheesh. Anybody with any ideas? It would be greatly appreciated. I know I've gotten a lot of use out of this machine (it's from 2007 so ancient really) but it was still running just fine and I am loath to spend money on a new laptop.