My 86 with 6.9 has 2 batteries, if I let it sit for one week, the batteries will be dead. So disconnected a cable from batt put amp meter on it, it has a draw of .12 amps. Can this cause 2 batts to go dead in 1 week?
thanks nick c

 

i'm not sure exactly .. how to calculate amp hours and draw correctly .. but if you don't drive it daily you could disconnect the batts from the truck circuitry but leave them connected to each other ..

and see how it does ..

if one battery has a problem it will also take down the other ..

and if an auto battery goes low enough to be dead .. it causes the plates to be oxidized when recharged and build up scale and then they don't take or release charge and you have a 'bad' battery from then on ..

they can permanently die after just one fully drained indecent or after several .. but every deep discharge causes some irreparable damage .. so it's likely the batteries are now on their way out at this point if they've been discharged a few times ..

so i would isolate and see if it's the draw or the batts ..

because you don't want to revive or replace them until you know if that draw is killing them .. then it would be dragging on the new batts also then ..

 

Put a SLOW charge on each battery, then LOAD test them.

You'll only get a meaningful ammeter reading if you disconnect BOTH negatives; otherwise the load will draw from the battery left connected. Re-do the current draw test with both negatives disconnected, and the ammeter in series on one of the negatives. Start pulling fuses one by one until the current reading drops. Then you'll have some clue as to your parasitic draw.

 

I did pull the fuses one at a time with no change. So I unplugged the one small wire going from the alt to the voltage regulator and the draw stopped. How would I determine weather its the alt or reg?
nick c

 

0.12 Amp * 24 hours/day * 7 days/week = 20.16 amp-hours for a week.
Assuming two std 50 amp-hour batteries, holding 100 Amp-hours, that would be about 20%. Not too much if they were 100% charged. But it could be a lot if they were only 50% charged.

check the alternator to see if it is putting out 13.2V+ above 1000 RPM
From the batteries perspective, the alternator is 'after' the regulator, and if the drain was just at the regulator, it should still be there with just the alternator disconnected. You should be able to measure that 0.12A between the reg and the alt. with your meter. Maybe rotate the alt. while measuring that current? I'm betting its the alt.

 

^^^^ Just from my reading of the forums, when there's a drain that goes away when you disconnect the alternator, the alt is the prime suspect.

I'm usually not one to throw parts at a problem, but a spare regulator is a good thing to have in your spares box, and small/cheap enough (compared to an alternator). Might be worth buying one just for that, install/connect it and see if the draw persists. If it does, that confirms the alternator as the culprit.