Slow drain on my battery

[Mike stoll]

So I just picked up a sweet 99 Explorer Sport....however the battery drains down slow ,I'm thinking it may either be the headlight relay or the auto dimmer switchaikovsky on the rear view mirror ,some timesay when you put the key into start the lights come on with the head light swith in the off position and stay on until the key is turned off...but if I fiddle with the mirror the lightsame will go on and off. ..any thoughts...?

 

[J_C]

In the worst case the mirror switch should just make the lights stay on for the longest timed interval possible. I forget how long that is but in the range of tens of seconds IIRC. It should not continue to cause battery drain. I mean if it were stuck on and heatlight still lit up, sure, but I doubt that's it if the headlights appear off when it's draining.

These vehicles have a battery saver circuit. Certain electrical components consume more power for a certain period, around 45 minutes IIRC, then settle down to about a couple dozen mA. That period starts, and is retriggered to start over at the full time length again, when some events happen such as opening the hood or door, turning on a light, etc.

For this reason the way to best test for parasitic draw is to open the hood, open the door, "maybe" close the door latch manually with the door open (I forget whether this is necessary, I don't recall it being necessary but it occurs that it might be in order to have the door open to access the interior fuse panel).

EDIT: lol, I forgot to mention the most important part, you're opening things you'd want open later so you can wait the ~45 minutes for the battery saver circuit to shut off and not retrigger it before proceeding with what is below. [/EDIT]

Disconnecting then reconnecting the battery will also reset the battery saver timer to the higher power state. Because of this, the way to test is to have a multimeter in current measurement mode and keep probes clamped onto the battery terminal and battery cable while you disconnect the two, so that the circuit is never broken between the battery and cable, conducting through the multimeter the whole time. Break that circuit and reconnect and you'll cause the battery saver to go into high power mode.

Anyway once you have the multimeter measuring current in the low power mode, observe the current reading as it should be roughly a couple dozen mA as mentioned previously. At this point you can pull out fuses on each suspect circuit to see how much the current changes. If the current drops from a pulled fuse on a circuit that has a relay after it then you might want to put the fuse back and pull the relay to see if that drops the current... could be the relay is bad, but then you will want to measure for voltage on the relay coil pin to see if (whatever) is energizing the relay when it shouldn't be on.

If you can narrow it down to a specific circuit then I might have a schematic to aid in further troubleshooting that circuit.

Another possibility is the battery is draining through the alternator, if it has a bad diode or voltage regulator in it. Similar to the battery to battery cable measurement you can take the alternator cable off at the alternator stud, put a multimeter between the alternator cable and alternator to see if there is leakage, except you don't have to be concerned about breaking the circuit before reconnecting it with the multimeter in current measurement mode - that won't reset the battery saver circuit timer and even if it did, wouldn't affect the battery to alternator measured reading. There should be zero current between the alternator and battery when the engine is off.

 

[Mike stoll]

J-C ,
Thanks for the advice,I'm going to get the meter out tomorrow and see what I find I will let you know what I find

 

[Mbrooks420]

The autodim mirror will keep them on well over a minute. If you slide it all the way to the left it should be ‘off’ and not turn them on, or delay their off timer.

 

[mic98xlt]

I would try disconnecting the autodim mirror by simply disconnecting the wire connector on the rear of the mirror itself. It has a single simply clip. The headlights will still work manually by the headlight switch as normal. This will eliminate the auto mirror itself as a possible culprit.

 

[wilto01]

The autodim on my 98 explorer stays on even if all the way to the left on off?
Do you guys have a fix?

 

[Mbrooks420]

The slider isn’t for the autodim, it’s for the automatic daytime running light timer.

 

[wilto01]

The lights stay on when the slider is off. Even in daytime.

 

[J_C]

^ If you're sure your dash headlight switch is switched off, the slider is probably worn out or corroded. You might try spraying some residue-free electrical contact cleaner (or mass air flow cleaner which is usually pretty much identical) into the slot and working the slider back and forth several times to see if that helps. However I don't know if any cleaners could cause damage to the mirror plate itself and would proceed with caution, trying to disassemble it to keep the cleaner only on the slider area.

If not then you'll probably be able to open it and clean off hardened grease and polish the metal slider contact, maybe put a slight bit more bend/tension in it if it's the stamped sheet metal type contact, and wipe the conductive tracks with a dry paper towel to fix it. Optionally and better would be to also put a tiny bit of dielectric grease on the tracks while it's open.

Other option of course is buy a new one or harvest a used at a junkyard... I might do that if it's cheap enough just to have one to pull apart and examine and clean before touching the one in the vehicle... some plastics don't like to come apart non-destructively once they get old and brittle. Warming them up first can help.

 

[wilto01]

Great advice and detail. Thanks J_C