Stereo wont come on

Check fuses them if all good Google what things aren't working. Did you cut any wire into you. Shorted something try putting a long wire on the battery hot side then take long end of wire to a fuse on one side put the wire then see if the things are working if so is fuse good you have an open you will find it

Has the battery been disconnected lately?

2001 Mitsubishi Galant Car Stereo Radio Wiring Diagram
Car Radio Constant 12v+ Wire: Red/Black
Car Radio Switched 12v+ Wire: Blue
Car Radio Ground Wire: Chassis
Car Radio Illumination Wire: Green/White
Car Stereo Dimmer Wire: Black/Yellow
Car Stereo Antenna Trigger: N/A
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Front Speakers Size: N/A
Front Speakers Location: N/A
Left Front Speaker Positive Wire (+): White/Blue
Left Front Speaker Negative Wire (-): Black/Blue
Right Front Speaker Positive Wire (+): White/Red
Right Front Speaker Negative Wire (-): Black/Red
Rear Speakers Size: N/A
Rear Speakers Location: N/A
Left Rear Speaker Positive Wire (+): Yellow/Blue
Left Rear Speaker Negative Wire (-): Gray/Blue
Right Rear Speaker Positive Wire (+): Yellow/Red
Right Rear Speaker Negative Wire (-): Gray/Red

look for a blown fuse in the fuse box

pull the radio back out and remove the wire marked dimmer control on the aftermarket radio then replace fuse

check the fuse box inside your engine compartment the fuse for your stereo is located in that box. or if your not familiar with it ask a automotive technician for a help

There will be a fuse, for after market radio's the fuse is in back of the radio, the radio will need to come out for fuse.

yes you should be able to hear it check the fuse box see if the relay is blown if not then you might need a
new fuel pump im not sure if the galant has an inertia switch or not i know some vehicles do and some dont

code stereo

not the right fuse.