Bad battery or a parasitic drain
There are a few reasons why a battery may drain overnight on a 1987 Cadillac Fleetwood. One reason could be the alternator needs replaced.
Happened to my 97. The alternator went out. Had to replace it and get a new battery. No problems since.
It could be two things. As you know, the alternator charges the battery so it will not drain. If the alternator is not working properly to charge the battery, the battery will continuously drain. Have the alternator tested at your local Auto Parts store (NAPA or Advance Auto) If it is good, have the battery checked.
If the alternator is installed incorrectly, yes, it can drain the battery.
No you sometimes need to charge your battery or get a boost if you battery runs low. Leaving your lights on for instance will totally drain the battery.
The key being in the "on" position itself. As for rapid battery drain, you could have a bad battery or there could be a loose connector. Source: Personal experience
Absolutely. If a diode shorts to ground it can drain a battery in a very short time.
Can be the battery has a dead cell which will require the battery be replaced. Can also be anything on the vehicle that is on pulling from the battery. Any light that is on or any relay that is stuck will drain the battery. Check under hood light, trunk light, glovebox light, interior lights, etc.
A dead cell in the battery will cause it to loose it's charge overnight. The only fix is to replace the battery. Any light that is staying on will drain the battery. Also a stuck relay will drain the battery.
A raidator in need of a flush will not cause a battery drain.
oil drain plug on cadillac sts42008
It might