Where is my input speed sensor located

I was told it is most likely the speed sensors and since there's input, output, and vehicle speed sensor they just ordered this part for me and said this was it pretty much lol. AutoZone. I probably am not even replacing the right part. I just recently had to take it to Mitsubishi and have them replace two wheel speed sensors due to ABS issue.

No clue. Sorry, I don't think anyone used the machine on it.

I went to both parts stores, since my check engine light isn't on, they said the machine won't find any codes.

Jesus! Haha. Okay, so I asked AutoZone why I got the input sensor when in pretty sure I needed the output. They claim there is no output on my year Mitsubishi, that when they search it, the only thing that comes up is the input. Ugh. This car is a pain in my A**.

The speedometer is acting very strange. It's different every time, sometimes it is 5 mph off or even 40 mph off. Sometimes when I stop at lights it still reads 5-30 mph, or when it is off it sits at 20-40 mph. All my other gauges and odometer still work fine. I was told it is a speed sensor on this site. My car only has input and output, I have called multiple auto parts stores, that's all that shows up other than wheel speed sensors.

Anyway, I bought and replaced the output speed sensor because I was told it sends speed to the cluster etc. Well, didn't work. $99.00 down the drain. The input shouldn't affect the speedometer I'm told, so should I just get a new "used" cluster?

Also.

I have flickering dome/headlights. My battery tests fine but it's also only four months old. My voltage shows 12.8 when off, when car running 13.5, and with all electrical stuff on it actually goes down to about 12.8-13.0. The auto store that did my test on their pricey machine claims that's fine, but I read if it was under 14.2 while running, then alternator needs replaced. Just need some help. Lol