.310mA is around what should be having... This powers the ECU, Alarm, Memory seats and HU Clock.
Seems that the battery was done for and the extreme cold just aggravated the issue.

Remember that most lead acid batteries are around +/- 40Ah that is around 40,000mAh so .310mAh while shut off is little to nothing for a normal battery.. 1A-1.5A though? that is a HUGE LOAD for parasitic draw and its what the faulty HFL Unit takes when it fails.

 

Herein lies my confusion - if the multimeter is set for 10A and I get 0.31 reading, is this 310 milliamps (not 0.310mA).

 

310 MA is high if it's constant. General spec is 30 to 50 MA over time. When you break the circuit to measure current and then complete the circuit by attaching the leads of your ammeter, many functions in the system do a reset and/or "Wake up" for a period of time. Leave the meter in the circuit for 15 minutes, key removed and doors closed. The current should settle down to below 100 MA at the most.


GOOD VIDEO HERE:

https://youtu.be/P-wxG6U5TuY

 

0.31 amps = 310 milliamps, which is almost certainly what the meter is reading.

 

Thanks. So obviously too much. Maybe I'll hook it up again and leave it for longer to see if more things go to sleep (as someone suggested).

 

No luck with waiting longer, but I did start pulling fuses and when F1 Backup is pulled from the engine bay fuse box, the milliamps drop way down. I've been googling...anyone have experience with the F1 Backup fuse and what other things might be on the circuit? Thanks.

PS, I pulled the bluetooth unit years ago when it stopped working, so I know it's not that (the HFL unit in the ceiling).

 

Whoopsie...never mind. I fixed it. I did indeed pull the original HFL unit years ago, and I baked it in the oven to melt the solder connections again. It worked for 2 days before failing again. The second time I baked it, I left it in the oven too long and all the little chips and resistors etc., fell off (lol..I know).

I forgot that I later went to a wreckers and pulled a unit from a wreck. It didn't work either, but I LEFT IT IN AND CONNECTED. I just pulled and disconnected it and - BAM - milliamps dropped from 310 to 20. Problem solved.

I'm kind of peeved now, wondering whether I needed a new battery or not yesterday. The auto parts store load tested my old one and said it was NFG, but I wonder if I had just charged it and fixed this power leak if it might have soldiered on. It was a Honda battery and about 2 years old.

 

Well at least we now know the F1 backup fuse powers the HFL.

 

That and a bunch of other things, apparently - interior lights, TPMS module (I think), Homelink....other stuff..