Don't totally dis-regard the battery being the problem. I had a 9 month year old battery in my old ford focus that went dead in less than a year. Sometimes it happens.
Check for lights (brake, dome, park) stuck on. If none, with the key off, disconnect one battery terminal and connect an ammeter between the battery post and battery cable to check for parasitic current. If it's low, say 0-50 Ma. there may be an internal battery problem. If it's well over that, something may be stuck or shorted on. Disconnect the alternator charging wire to check for internal short. If none pull fuses from the fuse panel one at a time to identify the problem circuit. If fuses don't stop the current draw, the problem may be between the battery and fuse box. Then pull fusible links one at a time.
When I'm good I'm very, very good and when I'm bad I'm HORRID.
There should not even be power to the engine fuse and the following C101 with the Ign Switch off. If there is B+ at the engine fuse with the key off it would seem there is an internal problem in the Ign Switch or it is not actually in the off position. Does your key pull out of the switch in any position?
When I'm good I'm very, very good and when I'm bad I'm HORRID.
Does your horn work? I bought a Mazda the did the same thing. Took me two days to track it down to the horn button. it was shorted and the relay was activated. Horn was unplugged.
'89L 110k mi. BP/G swapped
'90LX 68k mi. wrecked 12/14 RIP
'90 F250 4X4 108K mi.
'13 Kia Rio 5 LX 70k mi.
'18 Kia Soul 40k mi. Daily
'64 Studebaker Gran Turismo Hawk
'66 International Harvester pickup
second checking ignition, my ignition is jacked and if I dont make sure it is actually in the off position it will drain my battery. I can pull my key out in any position as someone else asked above as well as start the car with a screwdriver, definitely something to look into.
This is the short version on fixing my parasitic draw.
I disconnected the positive terminal of my battery. Hooked up the amp meter. Amp meter pegged.
Disconnected headlight fusable link. Parasitic draw went away. Reconnected link.
Disconnected c101 connector. Draw went away. This connector is between the battery and headlight below the relays. There are two connectors. C101 is the big connector. I took apart this connector and upon inspection found water and rust inside. This connector sits in such away that it holds water. I cleaned the rust out and dried the water out. I realize while cleaning that one of the pins was missing where the water sat. I applied dielectic grease to water proof inside the connector. Then I jumper pass the bad pin. This corrected the parasitic draw. I had some other electrical problems which went away after this fix.
My suggestion to everyone is to check this connector and water proof it.
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