98 Windstar Speedo/Electric/Power

I have a 98 Windstar and a few months ago the speedometer would stop working after about 3 miles of driving, then the transmission would stop shifting along with the speedometer, now I have the same problem but I loose power and the tranmission starts shifting on its own and all my lights on the dash start coming on and it will finally just die. when I try to start it again the battery is dead and I have to wait about 30 minutes to jump it. and everything starts over again. Is this multiple problems or one? I put a volt meter on the altenator and the output is 13volts aprox. I then tested levels at the battery and its 12volts. I took the battery out and it measures 11.8volts. thanks for the help in advance.

I have a 98 Windstar and a few months ago the speedometer would stop working after about 3 miles of driving, then the transmission would stop shifting along with the speedometer, now I have the same problem but I loose power and the tranmission starts shifting on its own and all my lights on the dash start coming on and it will finally just die. when I try to start it again the battery is dead and I have to wait about 30 minutes to jump it. and everything starts over again. Is this multiple problems or one? I put a volt meter on the altenator and the output is 13volts aprox. I then tested levels at the battery and its 12volts. I took the battery out and it measures 11.8volts. thanks for the help in advance.Hello gps1701,
How old is the battery,is the belt loose. A battery voltage should be about 12.7 volts. The alternator should putout 14volts. 13v is a little low. If your battery is 4 yrs old this could be a good time to replace it. Your alternator needs to be checked and they could do it free at a local auto parts store. As I remember Autozone might still do it. Good luck