Takuf150

I'm having trouble with my 1998 Ford F150 (4.2L automatic). The speedometer and odometer aren't working, and I'm getting the P0500 speed sensor code. I replaced sensors on the rear differential and output shaft transmission speed sensor, but the issue persists. Even after changing the instrument cluster, the speedometer and odometer still don't work. I've checked fuses, traced wires, and replaced the gear in the cluster, but nothing has solved the problem. I have cleaned all the connectors. I also have code P1506 code as well which is a high idle. My idle speed is 1200 to 1400 RPM of replaced IAC valve did a vacuum test nothing still high idles. Something tells me it’s a computer problem possibly. I’ve worked on German cars but never run into an issue like this before.

One thing that caught my attention is under the transmission; there is a plug and a speed sensor wire. It appears to be for the digital style cluster speed sensor wiring harness that connects to the transmission. I'm unsure if this is specific to a different trim level or if it could be due to a transmission replacement. Through my research, it seems like newer F-150s from '99 onwards have a similar setup. There's a possibility that the transmission was replaced, explaining the presence of the wire. Any insights or clarification on whether this is normal for my vehicle would be appreciated.

https://youtu.be/OCNQlwcqxxw?si=PkZt9ftqo1733dyS

my transmission has a plug on it.