DEI-OHD800B format usb

Maybe the video format on the USB is not compatible or supported by your LG TV. Look at you user manual for video formats that are playable via USB on your LG TV. If the video format is not supported you can use a video converter to convert it to one that it supports. You can use Free Video Converter by Freemake to convert your video.

not in backwards (battery) but led should not show as they are polarity dependant, didnt format the remote by accident somehow? any error msg on dash?

I think, it's the problem with music file's format please check the formats which your player is able to play and try playing those formats

Turn on FM modulator in OH monitor from the menu screen. Set station on screen, tune stereo to station.

Check the yellow wire, it has a 3 amp inline fuse. I have found that the inline fuse holder itself was defected and I replaced the whole fuse holder. You can find one at Radio Shack, Part # 270-1238.

http://search-manual-online.com/457cw-manual.html

the usb port is used to view pictures and videos off a computer or camera using the correct format

Check tack wire it has to be programed

You need dei part # 473T. The EZSDEI471remote is for older systems.

There is a white wire coming from the alarm, there should be a blue 15 amp fuse in that wire, close to the brain for the alarm. It sounds like you have blown that fuse.