Someone with a wheelchair or
ECV doesnt need a GAC to use it in lines.
The wheelchair stamp allows someone without a wheelchair to use a path that does not include things like stairs or allows them to board at a place where moving walkways can be stopped. These would be the handicapped or Mobility Access - as Disney calls them on their park maps.
Being able to use the Mobility Access might be important for someone who is able to walk fine, but cant do stairs or someone who is visually impaired and has difficulty with moving walkways, for example.
GACs are not given for specific disabilities; they are a way to tell CMs at attractions what kinds of assistance people need related to their disabilities.
Guests need to explain their needs to the CMs at Guest Relations to get a GAC.
Most attractions do NOT have a special different Mobility Access entrance. At most attractions, all guests enter thru the regular line and if the boarding area for guests with disabilities is not in the usual boarding area, those guest will have a pull off point to get them to the handicapped boarding area.
As for the other things that can be stamped on a GAC, exactly what happens depends on the attraction. Not all attractions have the same things available, so what happens at one attraction with that GAC may not happen at the next attraction.
Even the same attraction may direct guests to do something different at a different time the same day. This could be because staffing is different or the number of people with special needs is different.
Because of those things, it is not possible to say exactly what will happen with a GAC at a specific attraction. And, the different stamps or wording on stamps changes from time to time. We dont want to have things posted here and people expect things to work in a way that they wont work in the park.
For those reasons, we have some general information about what GACs are and how they work in post 6 of the disABILITIES FAQs thread. You can find that thread near the top of this board or follow the link in my signature to get there.
I am closing this thread now, since the disABILITIES FAQs thread about GACs has as much information as can be given.