1996 Questions for all other cars How to detect leaking curr

Electrical problem
1996 Questions for all other cars 4 cyl Front Wheel Drive Automatic

To whom it may concern.

Im living in Malaysia and Im currently riding a Malaysia National car which is a Proton.
Im riding a Perdana of Proton which is similiar/ exact to Mitshubishi Eterna model. A 2000cc engine with 4 inline engine. Auto tranny.

The scenario that Im facing is as per below:

My Proton Perdana is facing a current leakage in its wiring.
Due to this, it drains my battery flat (nearly empty).
This happened when I dont run my Proton Perdana for 3 days.
For the first two days, I start my engine early in the morning before I go to work (I go to work using 2nd car) just to get it hot until it reaches the operating temperature.
But on the third day which is today Wednesday, I notice my alarm sounds different as I unlock the door in the morning.
when I try to start the engine, it wont budge at all. NOTHING.
the battery is brutally flat out of voltage.
Check with an AGILENT U1252A Multimeter, the voltage that remains in my battery was only 3.5 volt out of 12 volt.
Did a jump start with my 2nd car and my Perdana is back to normal.
but in the evening, after came back from work, I try to start my Perdana back again, but it fails,
the battery is back to flat. So I assumed, there must be a leakage somewhere in my wiring.
Since Im no expert on electrical thinggy, Im seeking you help on how to detect the leakage by using a multimeter. What should I do and where do I start.
Just to mention, I would like to do it my self rather than sending it to a mechanic.
My concern is, what is the method to identify a leakage in a wiring system.
How to detect it?
Please advise.