There are probably several other causes, but I can only think of two others right now:
 This condition usually occurs when the engine is IDLING, and often is caused by the IDLE SPEED being TOO LOW.
 Slipping of the belt and/or pulley which drives the alternator can cause the same symptoms.
I suggest that you have a PROFESSIONAL AUTO ELECTRICAL TECHNICIAN, or any PROFESSIONAL [and well experienced] auto mechanic, check your problem out, and PROPERLY ADJUST the idle speed BEFORE any consideration of replacing an alternator and/or a voltage regulator.
If you simply replace these expensive components, AND THEY WERE NOT At Fault, then you will have WASTED a lot of money, AND you will STILL HAVE the problem, with more expense to come.
. Good luck.
Try applying parking brake
Auto headlights come on when it is dark. Daytime running lights are on whenever the engine is on. Both are optional equipment.
If you are parked with the motor running, engage the parking/emergency brake. Turn the ignition off and restart the engine. The daytime running lights should not be on.
13.8 - 14.4 volts DC,13.82 with engine running and headlights on!
no, using your headlights during the day, just uses power from the battery, and not from the engine, the battery is constantly being recharged , while the engine is running, any way,
If you have a voltmeter, measure the voltage across the battery, with the engine running. It should measure around 13 -15 volt (alternator is ok) now turn the engine off it should measure 12volt. If you do not have a voltmeter ,let a friend watch your headlights at night with engine running,than turn engine off, your headlights should go dimmer with engine off.
what causes aknocking sound on mazda T35 engine when its running
push the parking brake ,before starting the engine
If the engine isn't running, the battery is low. If the engine is running, the alternator probably has a problem. If you are wearing dark sunglasses, remove them and the lights will get brighter. good luck!
I take it you have daytime running lights , if so by engaging the emergency / parking brake the daytime running lights should go off
The lack of oil?!?