car off, battery drains overnight 1988 crown vic

hello, my dad has an 1988 crown vic ltd the car would turn off for the night everything would be shut off and the battery would drain almost comlpetely. he understands that it could be the altenator and his altenator is giving 13.80 to 14.20 but the car still will not start he also understands that it could be the battery but is there anywhere i could get an wiring harnes diagram for the car online and for free or could someone please help me out on this so that he can get it on the road soon? please help us out thank you?!?!

Leave battery disconnect overnight, if dead in morning then bad battery. If battery is still charged then a circuit in the car is discharging battery at rest. This is most commonly the voltage regulator on the alternator.

thank you! my dads has stated that the altenator is good and it has been rebuilt is there anything else other than the altenator and starter that could be the problem?

The alternator can be charging perfectly, however the integral voltage regulator often breaks down and leaks to ground. Put ammeter in series with battery lead and disconnect voltage regulator plug.See if current loss stops. Also check trunk,hood and glovebox lights that they turn off.