I bought a non working Switch yesterday for $50 with all the standard accessories. It was sold as non working because they said it wouldn’t turn on. They thought the battery was bad so they put in a brand new one. While playing around with it last night and noticed a very dark image on the screen. When I put it into my dock it came up fine on the TV and appears to play fine.
I tried draining it completely in handheld mode with a game running, and then plugging it back in, but still no backlight. Also, the right joycon shows no signs of life. I put it on my good switch and it doesn’t even try to charge. I do know that dead joycons can cause unhappy Switches, but even without any connected there still isn’t a backlight.
The console is a gray v2 and appears to be in excellent shape otherwise. What should I try? I seen it mentioned that the ribbons sometimes corrode.
If there is no back light i would either suspect the backlight ribbon, or the backlight IC. Given that the joycon is unhappy start by looling the the ribbon connector area as they are right next to each other
I opened it up this morning and went to clean the ribbons. When I removed the backlight ribbon there was obvious damage to one of the leads. I couldn’t clean in off, but rather it feels burnt or eaten away. I snipped the wings of the sides and snipped back the end of the connector so it could go further inside the plug but I’m still not getting any backlight. I noticed some discoloration of the pin that lead connects to inside the connector. I’m guessing either the inside of the connector is too dirty/damaged, or that the either the IC or the actual backlights went out. I saw a video of a guy repairing the ribbon by bridging the gap with a wire, but I don’t see how snipping it back wouldn’t work also.
I have photos to share but the website won’t let me 
It should let you post pics after a couple of posts. Corrosion can usually be cleaned off,or scraped off at least.
I tried to scrape but it felt it was indented rather than just surface corrosion.
Edit: still won’t let me post the pics.
The right joycon shows signs of possible water damage. Light corrosion on a couple of the ribbons and the water indicator is red. Might this point in me the direction of a blown backlight IC inside the Switch itself?
I would imagine it received water damage while connected to the switch, and that both the joycon and switch were affected.
It could be all 3, connector, screen and backlight IC, but i would start with the obvious and cheapest and go from there. So,if the connectors are a mess and cannot be cleaned i would replace them.