As i drive my battery loses charge to the point were the truck dies. Tried a new battery not that, tested alternator "voltage reg in alternator" test came back good so its not the alternator.
its a 90 mazda bseries truck.
Did you test the Alternator on or off the truck? It might be a problem with the control system to the Alternator. The regulator need a battery feed to work, It is usually ran through an alternator fuse.
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If a good battery is losing charge overnight then it is probably being drained by something left on! The usual areas to look at would be the boot light or glovebox light, check these or anything that might be staying on when the ignition is turned off!
Get out your volt meter and check the battery voltage, should be about 12 volts, then turn the key and see how far the voltage drops. If it drops below 9 volts or so, you probably need a new battery. Sniff around the vents of your alternator around fuse box, see if you can locate what actually fried..would suspect the alternator if this happened after driving the truck. The alternator charges the battery as you drive. If it is not functioning the engine will drain your battery until the vehicle dies, and probably wouldn't start even with a jump. Not real sure how to test the alternator without the truck running. Running voltage should be around 14 volts with a properly functioning alternator.
These are all signs of a bad alternator. The car is running off of only the battery. The alternator charges the battery and keeps the car running. When the alternator quits charging the car will run fine until the battery dies. Then you can jump the battery and charge it, and the car will run fine until all of the electronics and lights run the battery down again.
I am having the same problem with my 2004 Elantra. I have had the alternator tested twice and did replace the battery. This morning I had it running ad put a volt meter on it ( red to the battery pos black to the engine block) I did get a reading of 14 volts for about 30 seconds then the idle lowered and the voltage dropped to 12 volts. I tried this again later but could not get a voltage reading above 12 volts with the motor running. Any suggestions?
That sounds like an alternator. It is not recharging the battery as you drive. Seems you were driving around on just battery power. Have the alternator and the battery tested. And I would get a new battery since it has been drained and charged a couple of times.
The battery light coming on means the charging system cannot manage the demand on the system - i.e weak battery, defective alternator, bad regulator... Changing parts doesn't necessarily mean the replacements are working. Measure the voltage on the battery with the car running, you should see 13.7 to 15.1 volts. Turn on the headlamps, rear defogger, etc (put the system under load), you should stay in the same range. Assuming all of your electrical connections are good, the symptoms point to the alternator/regulator - these are integrated into one unit.
if you can charge the battery and drive it for a while then sounds like the altenator has failed and is not re-charging the battery, good way to test is to charge the battery, start the car and turn the light on, if everything is dimm or the motor dies there is little to no charge voltage, and will require altenator work
It appears that the alternator is still not charging the battery.Charge the battery up,and refire the truck.Check voltage with a voltmeter,directly off the back of the alternator.Most all alternators of your year model have the voltage regulator built into the alternator.If the alternator isn't producing any voltage,then it is bad,even if it is new.I have had defective new parts before.