Wiring for Check Engine Light

[Man In Black]

I think there is a problem with my check engine light on my 93 GMC K2500 pickup because the code reader does not work on the truck. The check engine light comes on with the key on and goes out when the engine is started but will not bring up any codes , not even the common number 12. I didn't hear the fans come on when the code reader was plugged in and the key was turned on and noticed that there is no electric fans on this truck. It has the old style conventional fan bolted to the water pump . Did this truck come this way or has someone changed something ? I want to check the wiring to the check engine light and the Haynes manual shows a white wire coming from the pcm going to one side of the check engine light and another brown/white wire coming out of the same side going back to the ( MIL CTRL ) on the PCM . Then another pink wire comes off of the other side of the Check Engine Light and goes through a fuse or circuit breaker to the ignition. ( Hot In Run ). Is this all that would affect the Check Engine Light and should there be electric fans on this truck to run when the diagnostics are plugged in and the ignition is turned on? Thanks for any help !