"2WD <--> 4WD" switch

Measure resistance between "b" and "c" terminals of 2WD/4WD switch.

If measured resistance is out of specification below, replace 2WD/4WD switch.

"2WD" <--> "4WD" switch resistance 

"2WD" <--> "4WD" switch released: 950 - 1050 Ω 

"2WD" <--> "4WD" switch kept pushing: 0 - 1 Ω