For 1990-2009 cars

The LH and RH side steering wheel controls, remotely control various functions of the radio. The steering wheel controls is a ladder network design consisting of switches and resistors. The network is arranged so that each switch has a different resistance value. An approximate voltage of 4-4.5 V is present at radio terminal F8 when the radio is On. The voltage changes at terminal F8 when a switch (e.g., volumn up or volumn down) is pressed. This input signals the radio to respond accordingly.

When the radio is turned On, battery system voltage is provided on radio terminal F3 to the steering wheel controls connector terminal A. This causes the LEDs in the steering wheel controls to illuminate. The ground circuit for the LEDs is provided at connector terminal D.