My 2002 Ranger 2.3l battery was dead. I found a battery drain of 1.25 amps with everything off. Pulling fuse #26 dropped the drain to 0.0. I've read about others with this problem but have found no one with the answer. I know fuse #26 powers the BSR, auxillary relay box, RCM, GEM and instrument cluster. How to I figure out which is the problem?

 

The 1.25 amp draw is normal just after key is turned off.
And yes pulling GEM/BSR fuse will drop that down

Your 2002 Ranger runs a 20-30min timer in GEM, timer starts when key is turned off and all doors are closed.
When timer runs out the BSR(battery saver relay) is opened and cuts power to all the systems except Keyless entry, Radio clock/presets and Computers KAM(keep alive memory)
This should be .03 to .07 amps

Testing this is hard

So first make sure Battery is not the problem.
After driving the truck when you get home disconnect battery positive cable
test voltage, should be 12.4 to 12.8volts
Let it sit for an hour or two
Test voltage again, may drop .1volts
Wait 20 minutes and test voltage again, should be the same as last voltage test, no change

If voltage is dropping then battery has a shorted cell, so is self draining, replace it
Most car batterys have 600AH, amp hours, which would mean at a 1.25amp draw it would take 20days to drain it dead, 10 days to drain it to 300AH
So even at 1.25amps it shouldn't go dead over night or even in a few days

New battery will show 12.8volts
3 year old battery will show 12.5volts
When a battery shows 12.2 volts, or less, it is done, will drain pretty fast and in cold weather it won't work to start engine

So it's not the battery
Get your amp meter out and a jumper cable
remove positive cable from battery
Connect jumper cable and amp meter to battery + and the + cable end
Turn on the key
resets timer circuit
Turn off the key and close all the doors
Remove jumper cable at either end but leave amp meter connected
Wait 30min to see if timer cuts power

 

RonD,

Thank you for the timely and thorough response. Since posting I've worked on the truck some more and believe I've narrowed the problem down to the battery. It appears to be draining internally -- probably shorted cells. I new battery went in the truck today and we'll see if it starts in the morning. The check engine light is on now and if the truck starts I will hook up my scan tool to see what it tells me.

All of this began when I replaced the thermostat (electric type). I doubt that one thing (the thermostat) caused the other (shorted battery) but I am curious as to what the check engine light is indicating.

More to follow. Thanks again.

 

Shorted cell is 99% of end of life for car batteries.

Batteries have plates inside, when discharging physical "pieces" flow from one plate to the other, that's what gives you the volts/amps that flow, when recharging these "pieces" flow backwards from one plate to the other, puts these "pieces" back so they can provide volts and amps again.
This flowing back and forth will create high spots on the plates, it also generate debris that settles at the bottom of the battery.
If one plate gets a high enough "bump" it will touch the other plate then battery starts to self drain, a short
If debris at the bottom gets high enough it will short two plates together.

So discharge/recharge just plain wears out a battery, and shorted cell is usual result with age.

Overcharging can also build up high spots much much faster, and also evaporates the liquid in the battery, the liquid allows these particles to flow back and forth so you lose full amp storage ability as liquid level decreases.

After new battery has been in place a few days, test battery voltage before starting engine, expect 12.8volts.
Then test it after starting engine, expect 14.8volts
Then after you get back home from a drive, don't shut off the engine
Test battery voltage again, expect 13.6volts

If you are still showing more than 14volts after a 10 minute drive then voltage regulator is bad, and that's why battery went bad

 

New battery has been in the truck for several days now and all is well. Clearly, the old battery was shorted and draining internally. Now I can work on the P1432 thermostat error.

 

Thanks for updating post and the fix