test the yellow wire for constant pwr, using the grn supplied in the harness.
thest the red wire for accesory pwr, using same groung again bot should read 12volt or around that give or take, if its less you have a bad connection, bad ground or a bad fuse that still is reading contnuity (sp)

if all else fail creat your own ground.

are you sure you didnt blue the radio?
To quick test
connect both the red and yellow wires together and then place the black wire to the NEG side of bat, then the coupled red and yellow to the POS+ side of battery, press pwr button, radio should lite up.
If it does go for the connection inside the car looking for same result.
-good luck