2006 12v battery fast drain

I just picked up a 2006 Prius that the previous owner said would drain the 12v battery. I purchased a new AGM battery and installed. It started and ran fine, but after shutting down it drained the battery in about 4 hours. I recharged the battery and then hooked a multimeter to the neg terminals and was getting between 1.9-4 amps of current, which indicates a big short somewhere. I systematically pulled all fuses and relays in the fuse box and relay box under the hood and none made any change.
Am I missing something obvious or is there something else that I can check?

 

Update, I unplugged the brake power supply box and saw a big decrease in the load. So, I left it unplugged overnight and went out this morning to see my battery still at 12.71v !
It's looking like that is the issue. I am going to pick up another box from the junkyard and see if it makes a difference.

 

Good point, and thanks for replying! I started thinking later that since it's been disconnected awhile those caps probably need a bit to recharge before I can accurately test again. However as I just posted, the battery stayed charged all night when connected but the brake power supply disconnected. I'll post more updates as I learn more.

 

Update, I bought a used brake power supply at the junk yard for $30 and installed. Next morning I still had 12.79v showing!
It appears this was the main issue with battery drainage.
Now on to other issues, like the combo meter display not working. It was working on and off when I got the car but now nothing.
I was able to take the car out on the road and drive and it drove fine. The multi display showed it was charging the hybrid batt but I still have the little car icon with the "!" in it showing.

 

New update: Today I went out and started it up and drove a bit. Dash still isn't working but "check engine" light and ! icon are gone.
Guess I'll try it again tomorrow and see what pops up. I ordered a new capacitor (as noted by others) to replace in the combo meter so will give that a try.
Also, today the stereo won't work in FM. It works in AM but no sound in FM but shows on the multi display. I'm assuming it's the amp but will look at that later.
The nav system kinda worked...kept freezing up so will have to play with that also.

 

Latest update...I removed the combo meter and replaced that pesky capacitor that everyone mentions. Reassembled and it now works! However, fixing one thing seems to cause more issues. Before: No backup camera, no combo meter, cruise control not working.
After: Combo meter works, Backup camera works, now beeps when in reverse as well as beeps when leave key inserted with door open.
But, Now when I hit the climate button, it says "check air conditioner connection". Also, energy display no longer shows motor charging battery, or braking or anything...just shows the wheels turning. Red triangle of death is also displayed. Now what? starter battery is new and showed 14v today. Tried disconnecting both batteries for about an hour but same result.

 

Thanks for your comments. I checked the voltage at the jump point this morning and saw 12.45v. I guess I'll take the dash apart today and double check connections and fuses. I still don't understand why the hybrid batt was showing about 80% bars and the car was showing energy back and forth before I "fixed" the combo meter and now nothing...No battery charge showing and no regen. Also at some point I saw the "B" option on the transmission but now that's gone. When I shift down it just beeps unless I move the lever over into D.

 

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Thanks for another reply! I felt like something had to be wrong so took out the MFD and found a loose wire on the harness that connects it. Gonna re-soldier and see what happens.

 

Well, that little wire was the problem. I soldered it back on and after reconnecting everything and powering up, I heard angels!
All of the warning lights went away except the TPMS which I assume is due to dead sensors. I took it on my first drive today and averaged 41.4mpg over a 44 mile trip. The hybrid battery is playing nice and all systems worked. I treated it to a nice wash today and a fresh oil change with 5w30 Mobil 1 extended performance high mileage. My next plans are new spark plugs and tires, possibly brakes. Anything else I should look at? I already changed filters. All axle boots and suspension bushings look good. and it drives straight and quiet. It has a Dorman hybrid pack so I assume it was changed fairly recently.
Thanks everyone for your assistance.

 

More great responses...thank you!
This car has 199k miles and unknown oil type/consumption so I was just playing it safe.