Dodge dakota trouble

My 4wd wont work in my 05 dodge dakota.
I flick the switch to high range and the light blinks
once then shows service 4wd and won't turn off
until i shut the engine off i tried it a few times and
it repeatedly does the same thing. I put it in 4 low
the 4wd low light  just keeps blinking and blinking.
I tried unplugging the wire connected to the
transmission and cleaned it out still nothing i
check the fuses there still good i don't know what
else to try anyone know what else i could try that'll
may help the problem ????