Stereo exposed to moisture stopped working new pioneer dehp500-UB

Could be speaker failure, especially if direct connection didn't work.

make sure the new stereo is compatible with the vehicle first before removing the stock one

check fuse inline with the red wire to the stereo, if no power check fuse box for power. of course, You will need a test meter for 12volts.

Loose connection on either speaker in pass door earthing out or broken wire from door to stereo connection

Apparently, you have no power at the 12 volt battery/memory wire at the radio harness of the vehicle. This wire is white with blue in color.
Also, based upon your description, you have connected the battery/memory wire and the accessory wire of the radio to the 12 volt accessory (switched) wire of the vehicle. This wire is white with red in color.
Check the radio/ stereo fuse of the car. You may have blown the fuse during your installation.
You have no memory at the radio because when you turn off the key, you lose all power to the radio.
Also, I mentioned the wire colors just in case you used an aftermarket radio wiring harness. Make sure that the yellow from the Pioneer unit is going to the battery power source and, the red of the Pioneer is going to the switched power source.

hold in the source button for a couple seconds see if that does it

clock setings

Check your connections to your speakers and amp and look for loose wires touching metal. I believe your stereo is fine, this has something to do with your speakers and the speaker wire

it is caused by moisture or by dust in it so you can clean it or if it is in warranty then it can be useful

the ''watts'' are peak or rms?notice that 150 Wpeak are about 70Wrms....
Also notice if you are using ''big'' speakers you can burn your amplifier..