start by sorting through the wires on the back of the stereo you should have
2 purple wires wich are back left speaker
2 green wires wich are back right speaker
2 white wires wich are front left speaker
2 grey wires wich are front right speaker
1 blue wire wich is for power areal needs wrapping in tape if not in use
1 red wire wich goes to ignition live ( the wire thats only live when the ignition is on
1 yellow/orange wire wich goes to the permanent live wire in the dash
and the black wich is ground any neutral wire or the chassis
to find the live wires ibn the dash put yer meter black wire on the chassis (anything bare metal ) set it to 12v dc then use the red wire to probe the wires for a permanent live when the ignition is off once you have found this thats where the yellow wire lives
then switch the ignition on and do the same again till you find another live wire wich wasnt live before thats where the red wire lives
connect those up accordingly then comnnect the black wire to the earth point either a wire or the chassis
once done the radio should come on with the radio on use the two purple wires to find a pair of speaker wires in the dash and continue with the other colours swap and change them to correspond to the right speakers being on the right wires with the balance and fade function on the radio
hope this helps just be carefull you dont let the live wires touch the ground or youll blow the fuse wich a good indicator will be that the interior light dont work anymore as they share the same fuse on most vehicles