I own a 1999 Mercury Sable and I am experiencing some electric problems. The car seems to turn over a little slow all the time. But car will start most of the time however sometimes when you drive it for 15 minutes and turn it off it will not start. It will turn over slowly and act like the battery its dead but if you wait a while it will start most of the time. Once in a great while the car will shut off when you are driving it and will not restart. The car has a brand new battery and the alternator was just tested and is good also
Sounds like abad cable or connection. You can check positive cable for corrosion if you can see it replace the cable as it is probably all theway down. Also check your ground connections. One other thing to check would be the solenoid, it may be bad and not letting all the battery load go through it.