electiccl problem

my girlfriends mother baught a 90 cougar. and now her battery keeps draining. she has changed the alternator and didnt work. i want to look good on this one, so if anyone can help. thank you.

Does the battery drain while the car is parked or while she is driving? Does she have any warning lights on the dash on while she is driving? Do all the warning lights work during startup? Do you have a wiring diagram? Some autoparts stores do free testing. Call to find out which ones, then have them load test the charging system in the car. Make sure the trunk light is not staying on.

Disconnect the battery neg. cable and take a 12volt test light clip the ground to the cable. Touch the neg. terminal if the light lights you have a drain on the system. You should have two relays that stick a fuel pump by the right trunk hinge and in the right kick panel. The older fords had an external voltage regulator which caused problems but I think yours is on the alternator.
If the relays are good pull one fuse at a time until the light goes out. But replace the fuse if it doesn't. When you find the problem fuse check what ever it supplies. Watch door lights go out or pull this fuse first. It is just a process of eliminating the good items until you find it. Hood lights,trunk lights and interior lights will stick some times.