@tamimd67, Since you bought this vehicle used. Please tell us what mods have been done by previous owners, if you know what the mods are. Probably you do NOT know. And have you done any mods yourself? These older generations DO NOT have any inherent battery draining issues.

Some possible causes:

• Aftermarket head unit
• Aftermarket security system.
• Bad short/wiring somewhere. Any signs of rodents?

bman

 

no sign of rodents. i think the grounds were checked. we don't know what mods may have been made, other than the stereo and amp that have been disconnected.

 

tamimd67

You should do a test to determine if you have a likely parasitic drain.
It's easy to do with an inexpensive basic meter that can read low voltage DC amperage.
These will also have other very handy tools for troubleshooting electrical problems.

To check for parasitic drain, use the meter to measure the current draw from the battery with the vehicle OFF.
Connect the multimeter between the disconnected negative battery cable and the negative battery terminal, and if the current exceeds ~ 20ma you have a misbehaving circuit.

Find the offending circuit by removing fuses one by one and checking the meter each time to identify the circuit, which when the fuse is pulled, will eliminate the current noted on the meter.

When the problem circuit is identified, you'll have a lot fewer items to track down where the problem is, which could be a component or the wiring to it.

Good Luck.

 

@DragonSubie7 Thanks!

 

If you bought the car from a used car dealer, even if you bought for cash, they may have installed a GPS tracker, which will be wired directly to the battery (if installed under hood) or to the fuse box or diagnostic port (if installed under the dash).
If present, these are usually easy to find. If found and removed, you may get a call from the dealer asking for the unit back. Provide appropriate expletive-deleted response.

 

It's possible that a GPS tracker was installed, but typical power usage is so low that it's not going to drain a battery overnight or even if the car is sitting for several weeks.

 

Faulty diode in alternator can drain the battery. Do a parastitic drain test as described above. You might even be able to feel some heat from the alternator in the morning if it was cold overnight.