1999 K2500 Classic 4wd indicator problem

[88sub4x4]

Hi all. I'm stumped. Trying to fix my buddy's truck. It's a 1999 K2500 classic (not a silverado) with floor shift transfer case. About a week ago his 4wd stopped engaging. I checked out a few things and found it would intermittently engage and the indicator light would illuminate. I changed out the actuator and now it engages every time the floor lever is put in 4wd. But....the indicator light no longer comes on. The 4wd is definitely engaging and disengaging when it should. I checked the bulb and it is fine. I also replaced the switch on top of the transfer case thinking maybe that was bad. I'm at a loss. What turns this light on? Do I possibly have a defective actuator? Thanks in advance for any help.

 

[DirtRidinz71]

I'm not positive on the newer ones with the electric actuator, but on my 92 with the thermal actuator it's pretty simple.
Power comes from the tcase switch when 4wd is engaged and goes to the actuator. When actuator fully engages it sends power back to the 4wd indicator light. It was as easy as a jumper wire to get the light to come on after the SAS swap with no actuator.
The newer one might have another wire for 4lo that goes to the ecm to control trans shifting when in 4lo.

 

[6872xtc]

I am fairly confident that there is a switch in the axle that tells when it is locked. I put a posi - lock cable on the front of my '95, and the light only comes on when both the axle is locked and the t-case is on 4x4. If I unlock the axle or go to 2wd, the light goes out. Maybe you have a problem with the wires or the switch for the axle lock indicator?

 

[88sub4x4]

There is no switch on the differential case that I can see that would turn the light on. I'm thinking it may be built into the actuator like dirtridinz71 mentioned. In that case I believe I have a faulty actuator. Does anyone possibly have any wiring diagrams that could help confirm this?