hello I'm new to the forum. I have recently purchased a 1990 gmc sierra k1500 and the 4wd will not work I have purchased a new thermal actuator and have voltage (12v0lts) at actuator connector. still no 4wd. my question is does the rwal have any bearing on 4wd operation. the brake light is on and was flashing and I have forgotten what the code was but could the rwal solenoid problem keep 4wdfrom working. thanks in advance for any help.