Answer to "2004 Ford Focus Radio problems..."Could be a fuse. There are two fuses for the radio. One for ignition off draw, and another for ignition on. There's a fuse panel in the knee panel below and to the left of the steering column. The fuse listing is on the inside surface of the cover panel, which is simply snapped in place.
Answer to "Why won't the screen show any readout?"I'm all for fixing stuff and keeping it working, but Harbor Freight literally gives these meters away. They're not worth fixing. i have a stack of spare ones still in the package waiting to be used.