my sisters ford focus 1.6 1999 , new battery keeps going flat took it to the garage they said it was the alternator got a new alternator but battery went flat again the day later they said the aternator and battery are fine cant trace the problem any ideas .i was looking at other questions on this site and some have said it could be voltage regulater were is this located on car if it has one and is not built in on alternator any other ideas about this problem most welcome thanks

 

I would start by starting with a good charge in the battery. Then shut everything off including the engine. Take an amp clamp and put it around the positive lead off the battery. Check for a load. If anything, it may register about 4-500ma. If you have any type of load, then start pulling fuses one at a time until the load goes away. That will be your culprit. I just did this on a Windstar that had a battery dying. The rear wiper was latched in the ON position causing a load, thus killing the battery. Found it by the above after the Ford dealer told my friend that it was either a bad battery or alternator and wanted a zillion dollars to fix... Cost my frien 2 cups of coffee and a repaired the rear wiper motor (cleaned and re-greased the gears).

 

If you don't have an Amp Clamp, go to local parts house and buy a test light. Disconnect either battery cable. Install test light between the disconnected cable and the bare battery post. If light comes on, you have a current draw. Follow Common's advice to find the circuit that is the culprit. Just be sure you don't leave a door open or any lights on.