Battery drain, Audio amp fuse

[Scott L]

Hi there,

I have a 2001 QX4 with stock Bose sound system which worked fine until recently. Actually, the Bose system itself still works fine, but if I keep the 15A Audio Amp fuse plugged in, the battery will be drained below starting voltage within 24 hours. What seems very weird is that with the fuse plugged in if I run an amperage test on the battery, after the car is closed up for 20-30 minutes the amperage draw will be around .03 mAmp which I assume is the clock, car alarm, etc. It will stay consistently at that level for many hours, but eventually when I check the meter, it will have changed to a draw of 60-70 mAmps. Note that nothing whatsoever has been changed or touched since the car was closed up. I keep the hood open in order to read the meter, and thats it. No door opening, unlocking, or any other input from outside. If I do the same test with the 15A Audio Amp fuse removed, then the draw never changes from .03 mAmp.

I spent many hours looking for a short without success, so finally wired a switch to the fuse so that I can effectively keep the fuse disconnected without having to remove it, and just switch it on when I'm driving in order to listen to the radio. That solves the problem, however I lose my radio presets, and if I forget to switch the fuse off, I'll end up with a dead battery.

I wonder if anyone has any ideas of what might cause this circuit to randomly create a draw on the battery with no outside input.

Thanks for any ideas.

[Mike W.]

I'm not sure on these, but pretty sure, they have 2 different hots going to the stereo. One would be constant on to run memory etc, the other switched with the ignition. Pull the radio, intercept the constant hot and put your meter or the switch in there. Unlikely, but it almost sounds like, something is going wrong in the stereo. Regardless, that would tell you if the drain is coming from there or elsewhere.

[macgiver]

Mike W is on the right track here , and I can add that USUALLY the B+ power to (All??) those Bose spkr mtd amps is ENABLED or switched via a relay . Find it , substitute w/another , for very weird behavious in relays - like in a very coastal ,salty E. coast environment some kind of rust / corrosion could be "bridging " a weird short.
So just like you removed a fuse , which you seem to have LOCATED the problematic area - again there should be a relay in that "area" to check out ??

I believe the relay is "Hot at all times" , AND energized (turned on/ switched) As the radio is turned on ,
now radio is "Acc on" and "Run" . IF the radio's signal (12v) to energize this relay DOES NOT SHUTOFF or "FLAKY" your gonna get the mA's / relays current draw . Relay amps (70 ohms) about 80 ma ? But an Amplifiers residual draw, that is w/NO source (quiescent draw) signal can be very Lo but significant ( H- bridge amplifier in these ; w/Mosfets ??)
Quiescent of 15 ma to 150 ma ??
Check it out !!

[Scott L]

Thanks to you both (Mike and macgiver) for your replies. I should have mentioned that at one point I disconnected all the wiring to the radio and the battery drain problem still occurred. As far as the relays are concerned, I may do some exploring in that area, probably with the help of someone with more electronic expertise than I have. I was/am hoping that someone might have a lightbulb moment about what the source of this was pretty certain to be, coming like a ghost out of nowhere after the car's been sitting for many hours.

[macgiver]

For example in my Bose system w/4 speakers , ea. has the little Bose Amps bolted to them. Now that relay which my CD / AM-FM head unit controls , is a "Double pole - single throw" . Basically an on/off serving two ckts from fusebox (15 A ea.) , whereas ea. 15 A serves a combined LF+LRr , other 15 A for combined RF+RRr. So in this case , for example ONE 15 A fuse powers two Bose amplifiers ie. a combined F AND Rr .
Very, very remote for a relay to have contacts "stick ON " , possible with HEAVY salt / chem condensations.Contacts may grow "crystalline-like" formations that can fully , or partially "Bridge" the contacts .Giving low resistance short up to a higher resistance short.

Not so remote for a Head Unit to have a weird fault which CONTINUES POWER to that relay?? Gotta realize most H-Units have the constant ( Hot at ALL times) memory/clock B+ connection - and the fault I mentioned could , very remotely possible to enable this relay ?? A weird short from mem power to the relay coil on your Bose amplifier(s) power relay(s) . So if you locate the "long storage fuse" which disconnects mem/clock power in order to store car for a longer "inert period" , Try disconnecting IT .

Lastly you got the "well intension" wiring job , from a guy , from trying an aftermarket H-Unit, from an aftermarket Adapter-Harness.... something there giving the relay (OR those little Bose amplifiers) JUICE when car is shutoff!!