LFA

1987 S4: We are trying to install an analog clock and replace the digital clock in the center console. The digital clock has 3 wires; 12V, ground and light. The analog 1990+ clock has this three connections and an additional fourth one in my 1991 GT ;which is +12V when the ignition is on . Why is there an additional +12V-ignition on connection on the analog clock, What if we do not install this and use the 3 existing connections of +12, ground, light.
Thanks for your help,