Adding 4wd indicator light - always hot?

[jus10inbrla]

Ok. As the title states. 93 k1500. Has the 4x4 on floor, and that lights up when 4x4 engages. I put another indicator in my cluster. Thinking to just tap into that wire, i tested . WITHOUT 4x4 being engaged, i am getting voltage on purple (wire 420) . Which makes my light illuminate. However, the light on the 4wd lever does not illuminate until it is engaged.

therese only 3 wires.. a ground, ilumination, & 4wd engage… so what am i missing?