2006 Ford Taurus: Replaced alternator , Battery light stays on

After replacing alternator in my 2006 Ford Taurus, the charging system lights stay lit while car is cranked. I took car back and had both battery and alternator checked again. Just my luck, another bad alternator. Replaced for a second time and charging system light is staying lit while car is cranked. I need assistance fixing my car. I can not afford to take the car to a repair shop, so I asked someone to install the alternators but this is as far as their knowledge will take them. Is there a guide that I might download to assist me in trying to repair my car? I am working two jobs trying to get back on my feet. This is not a warm and fuzzy feeling and concerns me with being dependable with my new jobs.

Please help. Thank you so much!

Mary