1992 4x4 button not working

My 1992 is having this strange problem. When I press the 4x4 button nothing usually happens. A few days later it may work it may not, very intermitent! I have tried thumping on the transfer case solenoid motor, ect.. when its not working but to no avail. Fuses and connections are good. Not sure about the 4x4 control box. Anyway to troubleshoot this, what is that white button/ red light on this anyway. Any help and advice is greatly appreciated!
Thanks,

Brian

On a '90 Ranger 4X4,you disconnect the five,and eight wire connectors(the flat ones),& w/ignition sw. in run pos.,push that button. A flashing light tells you the module is OK.A steady light is module failure.I have had the same problem You describe,and have never seen the module to be faulty. What I have found is the plastic connectors coming apart &/or the connection at the shift motor to be bad.

I had a similar problem, and replaced 4x4 switch. That did not work, and it ended up being that the wiring runs under drivers seat and had gotten "tore up" from adjusting seat. At first it would stick in or out of 4wheel, but then got stuck in 4 wheel until wiring was replaced at the dealer.