You should check the fuse first. If its fine, test the wire before the radio to see if its getting power.
alright i know nothing about radios so bear with me. is the fuse onn the radio its self or in the fuse box in the car?
The fusebox for your 74 is above and to the left of the brake pedal. My book says that on a 74 the radio feed is fuse#6 which is the one at the top right (20 amp). This is the fuse that also supplies the backup lights, windshield washer and turn signal flasher. I also show a "radio pilot" (whatever the hell that is) at location #3 (second from left on bottom row). It also supplies cluster lights, heater and a/c control illuminaton, windshield wiper control , ashtray and clock illumination. Some radios also had a fuse relay inline. It would most likely be a plastic barrel looking thing that's probably on a red wire coming from the back of the radio. Hope this helps.
