battery drain

[RustyTruck]

I did disconnect the alternator to check for any draw there and there was none. Battery is going back tomorrow. I charged the disconnected battery the other day and when I disconnected it, it showed 12.8 V. Dropped to 12.3 after 8 hrs.

Did you ever resolve this?

 

[J_C]

^ Welcome to the forum!

If a disconnected battery measures 12.8V (I'd give it a few minutes off the charger before measuring) then within 8 hrs, still disconnected, drops to 12.3V already, then the battery is bad, has the beginning of an internal short in one or more cells. If it was still connected to the vehicle electrical system, just use a multimeter to measure voltage drop across the fuses, or a DC clamp meter to measure alternator with engine running, or multimeter in current measurement mode in series with engine off to see if alternator has leaky diodes.

 

[RustyTruck]

Thanks for the reply! In my case I got a new battery and it still does it. I can see it's a 400mA draw that doesn't go away until the battery is dead (overnight will kill it). It's very frustrating. Some more data points for my case...

If I disconnect / reconnect the battery, there is no draw and all is well. Only when I "wake it up" by opening/closing a door, or pressing unlock/lock, then this 400mA draw starts and never quits.

When this draw is happening, I don't see any lights on, radio is not on, nothing seems to be left on.

If I remove one of the fuses for the instrument cluster, then the draw goes away. But unfortunately like half the vehicle's wiring goes through the instrument cluster for some odd reason, so I can't leave the fuse out.

 

[J_C]

List all the things on the circuit for the fuse # you pulled. Maybe it's something like an aux power or battery saver relay, could swap a questionable relay with another of same type in the vehicle to see if it makes a difference.

 

[CDW6212R]

Ditto, I'd suspect a relay. I had a fog light relay in my 98 Mountaineer that was tripped closed, the fog light were on constantly. Those are located low in front under the air cleaner, the high humidity probably did it in after 20+ years.

 

[RustyTruck]

Thanks for the replies. The only fuse that would completely stop the power draw is the vbatt one going to the Instrument Cluster.

I pulled the battery saver relay and the draw would lessen a little, but there would still be enough to kill the battery overnight. I tried pulling every fuse, every relay that I could find, but the only thing that I could find is the Instrument Cluster causing it. I see there are services that can rebuild them (possibly fix it), but for now I'm going to change the Instrument cluster to be powered by key-on instead of on-at-all-times. It's a little annoying because the gauges do the little power on dance for 10 seconds now when I turn the key, and the interior/bed lights no longer work without the key being on. Will try it like this for a bit though.

 

[J_C]

Does your battery saver relay come on with any activity like opening a door, then say on for ~45min or so? If it does then it seems like it might give you a little more time and less grief to tap into that rather than the ignition circuit. It would of course drain more power for the 45min the battery saver is live.

 

[CDW6212R]

Has the interior lights ever been on after you lock it up? The door latch switches will run the lights if it doesn't sense it being fully closed, a bad striker bushing can do that.

 

[RustyTruck]

Does your battery saver relay come on with any activity like opening a door, then say on for ~45min or so? If it does then it seems like it might give you a little more time and less grief to tap into that rather than the ignition circuit. It would of course drain more power for the 45min the battery saver is live.

This sounded like a great idea, but i found in my vehicle the Instrument Cluster actually powers the battery saver relay - so I can't tie the Instrument Cluster to it (like a circular reference or something)

Has the interior lights ever been on after you lock it up? The door latch switches will run the lights if it doesn't sense it being fully closed, a bad striker bushing can do that.

Great question. This was working ok - when I lock the doors, the interior lights would go off right away.


For now, I'm going to put it all back together and try it with the Instrument Cluster moved to the key-on circuit instead of being on all the time.