Speed Sensor
Disconnect sensor wires from amplifier and connect an ohmmeter between wire connector terminals (green & black). A reading of about 40 ohms should be obtained. A reading of 0 ohms indicates a shorted coil and a maximum reading indicates an open coil. Replace sensor in either case. If reading is 40 ohms and speedometer operates properly, speed sensor is probably good. A new sensor should be substituted in place of old sensor to check for proper operation.