How do I know which multifunction switch I need. Not sure if my truck has cruise control or not. This is my first Chevy. The switch was gone when I bought it. There are 4 wires : yellow , blue , red and green

 

Look under the hood - if you have cruise control, there will be 2 cables attached to the throttle body. One leads to the gas pedal and one leads to the cruise control module, which should be mounted on the driver side firewall.

 

The pic looks like a non cruise control switch, just works the wipers.

 

I see you have the old style interior (1988 - 1996, if I am not mistaken). I have a '98 and the cruise is a 3 position switch on the stalk and a button on the end. I would assume if yours had the same setup, if you had cruise, their would be a hole on the end of the stalk where a button used to go. I could be completely wrong, I do not even know it those years had cruise control, I assume they would but that is about it...