Battery light stays on
- Thread starter doolah02
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Go to harbor freight and get a free meter. See what its charging at for starters.
Use a multimeter, measure battery with engine off (should be around 12.6V if the battery is good). Measure with engine on, should be around 14.4V if the alternator is good.
Do you have battery voltage at the big wire on the rear of the alternator?
You wrote the battery is ok but how did you determine this? At quote "alternators were charging" (presumes engine was on?) 12.3V it seems very low. That is 2.1V below where your vehicle electrical system should be (should be 14.4V with engine running and a good battery), so my greatest suspicion is your battery has one cell failed and this is causing your alternators to fail.
If the battery is not a maintenance free type (has caps you can remove to add water), check the water level. Top off with distilled water if any are low. Using a multimeter, put pieces of solid core copper electrical wire on the multimeter probes, wrap them around the probe end then a few inches of wire extending beyond the probe end, so they become sacrificial so battery acid does not eat your multimeter probes themselves.
Stick them in two adjacent cells to measure each cell's voltage. There should be a 2.1V reading between every two adjacent cells. There are six cells which is why 2.1V x 6 = 12.6V for a fully charged battery. A zero reading means the cell is shorted and the battery should be replaced. Make sure your meter probes and the wire don't come loose so you don't get a false 0V reading due to that.
It is probably easier to do than explain but I'm sure there are youtube videos and other resources if I have not made it clear enough how to test for a shorted battery cell. The other deductive way to test, especially if it's a maintenance free type with no access to the cells, is put it on a charger (but carefully monitor the charger to make sure it does not overheat! You may have to charge a few moments at a time and let the charger cool down if it is not a design that is overheat protected) then take off the charger and let it sit for a minute. If it reads 2.1V low (closer to 10.5V instead of 12.6V) you have a shorted cell.
If the battery is not a maintenance free type (has caps you can remove to add water), check the water level. Top off with distilled water if any are low. Using a multimeter, put pieces of solid core copper electrical wire on the multimeter probes, wrap them around the probe end then a few inches of wire extending beyond the probe end, so they become sacrificial so battery acid does not eat your multimeter probes themselves.
Stick them in two adjacent cells to measure each cell's voltage. There should be a 2.1V reading between every two adjacent cells. There are six cells which is why 2.1V x 6 = 12.6V for a fully charged battery. A zero reading means the cell is shorted and the battery should be replaced. Make sure your meter probes and the wire don't come loose so you don't get a false 0V reading due to that.
It is probably easier to do than explain but I'm sure there are youtube videos and other resources if I have not made it clear enough how to test for a shorted battery cell. The other deductive way to test, especially if it's a maintenance free type with no access to the cells, is put it on a charger (but carefully monitor the charger to make sure it does not overheat! You may have to charge a few moments at a time and let the charger cool down if it is not a design that is overheat protected) then take off the charger and let it sit for a minute. If it reads 2.1V low (closer to 10.5V instead of 12.6V) you have a shorted cell.
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^ No the regulator for an '01 Sport Trac is built into the alternator.
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