The first thing is to tune into a strong station. These radios are very dependent on the strength that is presented to the antenna terminal. If you are using an antenna on the truck, raise it as far as possible for testing. If you are in a garage with metal cladding, try moving the truck outside. Sometimes the signals are much stronger later on in the evening. One other thing is that the new solid state vibrator replacements are very sensitive to supply voltage. Sometimes it is necessary to have the engine running and the generator actually showing charge to get the radio to work properly. That provides an input voltage to the radio of over 7 volts.
