how can you tell that alternator does't work
If it is getting food stamps, that is a pretty good indication.
Have it tested at a local auto parts store such as O'reilly Auto Parts or similar. This is a free service.
The battery light might be on. If you have a voltmeter the voltage would be below 12.5V and dropping.
Looking for a Used Edge in your area?
CarGurus has 56,714 nationwide Edge listings starting at $2,995.
Search Ford Edge Questions
Ford Edge Experts
Related Models For Sale
Used Cars For Sale