if the cabin light of your car is on without the engine running, the car battery will drain after a few days. but usually someone will notice it at night and inform you so you can switch it off or make sure all the doors are properly closed. or if you use your car daily the car battery gets recharged when you drive the car.
(photo 1) but if you don't use the car daily and put a car cover on the car, then if the cabin light is on, nobody will notice it and your car battery will drain. this is what happened to my dad's z3. while they were away, i covered the z3 and not used it because too many girls already chase after me. it's the downside of being too handsome.
the first troubleshoting step i did was i had the battery recharged.
(photo 2) i then tested the battery and alternator using the tester i got from lazada for P200. both were ok.
(photo 3) then i used a test light (P150 in lazada) to check for parasitic drain. the light lit up which means there is a parasitic drain. however, this does not mean there is something wrong because cars with computers will always have an allowable 35mv of drain.
(photo 4) my 1993 sentra has no computer so the test light did not light up when i tested my tesla for parasitic drain.
to find out the amount of drain on the z3, i asked my babygirl to buy a 1 ohm 10 watt resistor (P12) in AC/DC colon and some alligator clips (P15).
(photo 5) the store did not have an alligator clip big enough to clamp the battery terminal so i just clamped the negative terminal with a jumper cable then clamped the thin metal part of the giant jumper clip with the tiny alligator clip.
(photo 6) to securely connect the resistor leads to a wire, i spliced one end of the wire and WOUND each STRAND one by one to the resistor lead. then i BENT the resistor lead to prevent the wire from sliding off.
(photo 7) then i connected the resistor in series with the negative terminal of the battery and checked the voltate across the resistor. it read .69v or 690mv which is well above the allowable 35mv drain (the digital multimeter is P792 in lazada).
the next step is to remove the fuses 1 by 1 to check which one is the culprit. my dad suggested i remove the fuse for the cabin light first because that's the usual cause. my dad was correct. the voltate dropped to just 7mv when i pulled out the fuse for the cabin light. however the high drain could be caused by the baggage compartment light being on because the baggage door is opened.
(photo 8) so i re-inserted the fuse and closed the baggage to turn off the baggage compartment light. the voltage also dropped to 7mv, which means there is no parasitic drain or there is nothing wrong with the z3.
i realized i must have accidentally hit the cabin light switch and set it to the on position while i was fixing the rear view. i did not notice the cabin light was on after i fixed the rear view mirror because of the bright day light. or maybe the doors were not properly closed which keeps the cabin light on. nobody noticed the cabin lights were on at night because i covered the car.
the moral of the story is if you put a cover on your car and don't use it for many days, make sure the cabin light is not on.
(for more of my knowledge bombs, click the "ian's knowledge bombs" banner at the top of this article and choose any article in the table of contents that piques your interest)
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