Look at your front axle assembly. On the passenger side of the diff, you will see a vacuum actuator with two vacuum lines going to it (provided it has not been modified). That vacuum actuator slides a fork which in turn shifts a collar inside the axle tube to lock the two piece axle assembly together. You should also see an electrical plug coming off the side of that actuator assembly. When the shift occurs, a switch closes and the light comes on. Only one color of light. No different colors for 4 hi or 4 lo. If the axle has been converted to a solid axle then you will find a blank off plate where the actuator used to be.