HELP! 12v battery parasitic draw not in any fuses

HELP! I have a parasitic draw on my 12v battery of ~90 ma but I realize the resting current draw should be closer to 20 ma. When I have a multimeter in series and remove each fuse in the fuse boxes (engine compartment and under instrument panel), I can only determine three fuses that result in a total draw of 10-20 ma in resting state [fuse 12 (ACC-B), 28 (H-LP HI RH), and 39 DOME]. I cannot determine where the remaining ~70 ma draw is coming from. Are there other circuits that are not on these two main fuse boxes? How else can I determine where this draw is? I pulled many relays as well (no effect) but I assume those should just be embedded in the circuits with fuses.

BACKGROUND: I have known that the 12v battery in my Prius had an appreciable resting state current draw since I got it 4 years ago because the car would go dead when simply parked for >1 week. I thought it was just the way Prii (Priuses) operated. Part of the problem is that I'm an occasional driver (avg <3000 miles/yr) as I don't have a commute and am away a lot (I work internationally for 2-4 weeks at a time). An initial attempt to jump start the car with my truck battery was disastrous and blew some fuses, but all was restored by a specialized Toyota mechanic (TLC here in San Diego). Since then I realized that special jumping was needed and I bought and used a Suaoki 12 amp-hour external electric jump starter whenever I needed to jump start the car. I also bought a Black&Decker 3M3B battery tender but didn't use it very often (car is not garaged). I addressed the issue of the car being parked long spells by disconnecting the 12v battery in the back when I would go away for more than a week. I replaced the 12v battery sometime in 2016 soon after I got the car with an equivalent AGM Optima from Napa (I also had fixed the hybrid battery). However, unfortunately I let that 12v battery go through several discharging cycles, and I had to replace it in 2017 (under warranty). More recently I replaced it with an OEM TrueStart battery from the Toyota dealer (about 5 months ago; ~$260). Around that time I also bought a 20W 1.3a solar trickle charger which has generally maintained a good charge state on the battery even when parked for long periods of time. Recently with less sunlight as I was occasionally checking the voltage of the 12v battery, I've noticed that even with the daily solar charging, the 12v battery was slowly declining in voltage - such as morning readings of 12.40v, then 12.35v, then 12.30v, down to 12.2v (I charged up with the battery tender at that point). I realized from this forum that it seemed it the 12v battery was dying too quickly in the resting state so I decided to try and figure out if and what the parasitic draw was, and address it.

CURRENT DRAW MEASUREMENT: I disconnected the 12v battery and hooked up a multimeter tool to the negative (black) lead in series, and measured a ~0.09 amp current draw when car was at rest (>5 min no disturbance except hood open; key >20 ft away; doors unlocked; but I noticed that locked doors didn’t have any effect). Actually it would vacillate sometimes between 0.08a and 0.09a (or the following day from 0.09a to 0.10a). When a door is opened, the current draw goes up to ~1.9 amp, then starts to go down some, staying at ~0.7 amp and remains there presumably from lights being on. If the door is closed immediately, it remains at ~0.7 amp for 10-20 sec, then goes down to the original resting level (0.09 amp). If I approach the car with the fob, the current draw sometimes goes up to ~0.65a. Locking or unlocking the doors brings a brief (~100 ms) current draw close to 10 amp but the multimeter handles it without wrecking (the max the multimeter can sustain is 10a). Having the voltmeter connected does not appreciably affect current draw (it stays ~0.09a). The TrueStart battery capacity is nominally 45 amp-hours and it's only ~5 months old, purchased from a Toyota dealer. So theoretically with a 0.09a draw, it would drain 1 amp-hour every 11 hr or so, or about 2.3 amp-hours per day, and would take ~9 days to discharge 50% and 18 days to completely discharge. However, I've noticed sometimes that the voltage drops from 12.7v to 12.4v overnight which suggests maybe the capacity of the 12v battery is not the full 45 amp-hour or that there is some other drain on the battery at night.

FUSE CHECK: I kept the current at the stable ~0.09a parasitic draw and pulled individual fuses to determine which circuit affected the current. There are 2 fuse boxes: one in the engine compartment and the other below the steering wheel on the left. When checking the latter, the doors must be closed and someone reading the multimeter when pulling the fuses (my wife helped with this). I used needle-nose pliers to pull each fuse and see the effect on the current reading going through the multimeter.
Pulling most engine compartment fuses has no effect except the following:
FUSE 28 H-LP HI RH (right headlight/highbeam): changed multimeter reading to ~0.08a (maybe drawing up to ~0.005a)
FUSE 39 DOME (audio, smart key, interior lights, luggage light, clock): changed multimeter reading to ~0.08a (maybe drawing up to 0.01a; also noted that when reinserted this fuse, the current went up from 0.08a to 0.13a, then settled to 0.09a]
FUSE 12 (ACC-B Power Outlet; “ACC” fuses): assumed multimeter reading slightly down; the current goes up to 0.11a when this fuse is reinserted and may drop almost imperceptible when removed

SO WHERE IS THE PARASITIC DRAW OF ~70ma? What else can I check to determine it?

 

Good point. Is there a way to edit or delete? [I can repost just the first part]

 

Thank you so much for the reply to my long initial post! To respond, if all 3 of those fuses that I mentioned are out, there is still a current draw of 0.07-0.08a. I appreciate the suggestion that some other circuits without fuses could be the culprit. I was looking into the fusible link block as a potential culprit and may try to pull that out. My diagram shows it by the 12v battery. I also appreciate the circuit diagrams. [I do need to review the diagrams more closely] Do all these other circuits go through the fusible link block?

I also realize that there may be some unintended current path. That seems like it might be harder to determine/locate. But just FYI - the car wasn't reverse jumped, I think the amount of amps that went into the circuitry from my truck battery (I connected it to the 12v battery and not the leads under the hood) were too high and fried some of the fuses. Apparently that's why they say never jump start a Prius from a regular car. Regardless, there might have been some melting of something and current leakage due to it. I'll try some to diagnose some more and report back.

 

I also realize there is another "fusible link" in the engine compartment fuse box - something I didn't check yet. I saw a thread here about removing and replacing that - sounds a little involved. I'll try to disconnect that as well to see if it's the source of the ~70ma current draw.

The "fusible link block" on top of the 12v battery is easy to disconnect the wires from.

 

Thank you for more input. You may be correct that I did a reverse polarity jump. The truth is I don't remember exactly what happened as it was 4 years ago. I looked at the TLC mechanic receipt to remind me - it says that I reported the car wouldn't start but radio turned on, so I tried to jump it under the hood and at the battery terminals, but during one of those jump attempts the jumper cables got very hot so I stopped (I recall the plastic coating on the jumper cables melting!). The car was completely dead, and then I was quite happy when the mechanic easily fixed most problems by replacing 2 fuses and the "fusible link block" (a $260 job). [I think he probably meant the "fusible link module" in the engine compartment?]

I did pull those connectors coming from the fusible link block by the 12v battery. With the big one pulled, all current went to zero. I realized this is expected since all circuitry powered by the 12v battery goes through that connector.

I then went to disconnect the fusible link module located in the main fuse box in the engine compartment (photo). When I disconnected the main wire into it (located just left of and closer than the red cap for jumping access - it's the one with the big metal loop), I saw that the current went to zero. I initially thought this narrowed the current draw to the fusible link module, but current went to "0" and not to 0.02a, so I suspect some current going to the rest of the fuse box is passing through that wire.

In addition to the main wire at the top left side, there are four bolted wires on the sides of the fusible link box and other wires connected on the bottom. I'm trying to get the module out to disconnect these one by one but I'm having a tough time getting the connected black fuse box part out as well (stuck at the closer/bow part of the black box). Seems like it might be difficult to pinpoint it further within the fusible link module. I might be able to disconnect some of the bolted wires but it's not clear all the fusible links they connect to.

 

Thank you RJParker for all the informative help! I got the fusible link module disconnected from the black fuse box buss bar. Without pulling out the black fuse box part entirely, I was able to lift out enough of the fusible link module to remove three of the more easily accessible cables that were bolted to the box (two on driver's side between the two tabs, and the one on the passenger side). I determined that through those cables there was probably ~15 ma draw since the current from the battery dropped to a stable 0.08a from 0.09-0.10a. I didn't determine which of the three its was coming from. I figured this was an insignificant parasitic load - I was still looking for the 70ma draw.

I also realized that the buss bar to the fuse box passed current that controlled the locks and some other functions. My fob key would not work to lock or unlock. I actually had to push down on the back hatch to close it enough to get the stable lower 0.08a reading from the multimeter in the back.

I was about to give up, but gave another shot at getting the black fuse box part out and eventually did. With that out, I could lift out the whole fusible link module. The difficulty stemmed from the black fuse box staying attached at its front part - I couldn't figure out where the tab was that was holding it in. Eventually I did - the tab is hidden down under, around and in between what look like the two black tabs there - and you have to push it in from an awkward position. I was then able to remove the fourth cable bolted to the fusible link box, which I determined had no effect on the ~0.09a current.

I was going to pull the whole fusible link box out and then pull each of the inserted bottom cables, but I would have had to remove all the bolted wires again and it just seemed like it wasn't going to result in very useful information for me. I suspect that ~70 ma draw is from some of the bottom cables coming out of the fusible link box. I assume you can tell from the wiring diagrams what those bottom cables lead to? I'm just curious what it might be - could possibly motivate me to take them out or to assess the systems powered by them. Having gone through removing and reinstalling that fusible link box is something good to know. And although it would be nice to resolve this issue, you're right that it seems to be getting too involved to chase down - just to resolve a relatively low parasitic draw that I have lived with for many years now and can until I sell the car. [I'd love to upgrade to a Plug-in Prius].

 

Also, as a note to EdTheFox and others, I found a great 467-page document of the entire detailed circuitry of the 2nd gen Prius online at:
http://www.selidori.com/tech/00000-04999/337-aBgux.pdf

For removing/changing the fusible link module, there is a good post with photos here on PriusChat and also a video on YouTube:
How to change Fusible link under hood | PriusChat

[A final note - although I took electromagnetics in high school and college physics, I'm no electrician and it still seems pretty complicated to understand where all the circuits connect - unless you really know each symbol by heart and can figure out easily to/from connections not shown on the page]

Many thanks to all contributing to this forum and special thanks to rjparker and edthefox here for the guidance.