Independent vs Dependent Rocker Switch Lamps
Whether LED or Incandescent, there is a fundamental difference between Independent vs Dependent rocker switch light types. The root of the question is how is the lamp triggered (illuminated):
An Independent lamp can illuminate “independent” of the rocker switch’s position. Meaning that the switches does not HAVE to be ON for the lamp to be on. It will necessarily have a separate power input just for the light, and is commonly used for backlighting the switch. Backlight power usually comes from another switch like: head lights, Dash lights, Navigation lights on a boat or your ignition.
A Dependent lamp only illuminates when the rocker switch is ON. So this type of lamp usually functions as an indicator light. A dependent lamp will have wiring internal to the switch that forces it to always illuminate in that position.
Our rocker switches may have none, one, or a combination of independent and dependent lamps. A common combination for instance is an independent backlight at the top, and a dependent indicator light at the bottom (like this switch). This way the top illuminates the text and/or symbol when your head lights are on… and the bottom oval lens illuminates to tell you when the switch is on.
See wiring diagram below for the V1D1-G66B, which has both an independent (top) and dependent lamp (bottom). Blue lines indicate dependent circuit and red the independently triggered backlight (via terminal 8). They share a common negative terminal (7). Now the dependent circuit is tied into an external terminal (3), but that is also the terminal for the output of the switch (thus, dependent upon the output).
If you think about this for a minute, there’s another way you could wire it. What if you put power into terminal 3, and output of terminal 2? You’d have a situation where the dependent light is always on when power is applied to the switch. Now, if you jumped terminal 2, up to terminal 8 (in parallel with the switch output)? Now you’ve turned the top independent lamp into a de facto dependent lamp… so the bottom tells you when source power is applied, and the top lamp now acts as an indicator for when the switch is on.
Make sure you design your custom actuator appropriately for the type of switch body it’s going to go onto (more about that here). Otherwise you could end up with a light behind the switch that cannot be seen, or a lens with no lamp behind and can never be illuminated. Each rocker switch body’s product page will tell you if you need a bottom lens or not.