Your cruise light worked with the later PCM with the early dash cluster?
Yeah, that's the general consensus. Most folks who swap in a 421/422 PCM into a 401/402 truck get a cruise light.
I know we've been over the wiring, Matt. So I'm going to actually find out with a voltmeter what is going on with the E99 PCMs that are physically wired and even have a PCM pin specifically for the cruise light..........but no cruise light illumination. My guess is that the hardware is there to light it up, but no firmware to turn on the transistor when there is a cruise control activation. The E99 PCMs must just not be able to turn it on....and it was an oversight by the engineers that programmed the PCMs. Obviously since the E99 trucks HAVE a "cruise" light in the cluster, the desire was there.