These two answers came from another site.
See this is what type of answer I was looking for, No BS. Was not programming anything, just wanted some more information on how things work.
The radio usually will attempt to register when first powered up after it seeks a control channel (if programmed for the first time) or will go to the last control channel it was on when powered off. Once it decodes the system ID and WACN and verifies they match, then it transmits an affiliation request along with it's stored individual ID to the controller over the CC.
Usually you will see the red TX LED flash once or twice when this happens, the radio once affiliation is complete will then be given it's WUID and will either be allowed to receive traffic on that talkgroup or not (all depends on how the radio's ID is setup in the Provisioning Manager). If a radio is set to passively inhibit, it would occur at the moment the radio attempts to affiliate.
Whenever you change talkgroups, go in/out of scan, or the radio re-scans control channels. it will send data to the controller again. In an Astro 25 environment, if the ID is invalid you will usually get a SYS REG REFUSED message on the subscriber radio if the affiliation was not successful if no radio profile exists and the DEFAULT profile is disabled. Your radio will not receive any traffic at that point.
You'll see the xmit light flash as it attempts to transmit. If it flashes quickly several times one time, and then not again for a very long time, it succeeded in affiliating. If it keeps flashing, then it is not successful, and may display an out of range message. OTOH, if it never flashes, then someone programmed it for non-affiliation which is what unauthorized users should be set to.