LAST EDITED ON Jun-22-03 AT 09:35 AM (EDT)
The voltage regulator is internal of the alternator. From a previous thread...
Testing your charging system quickly with a digital voltmeter (assuming charged battery):
1. Test battery voltage with engine off. Check at battery terminals at clean terminal or clamp, not the bolt or nut. Record voltage. This is your battery's standing voltage.
2. Start engine & run at 1500 RPM. With no other load (doors closed? Underhood light off? Auto headlights off?) - record voltage. Voltage should be higher but not by more than 2 volts. This is your charging voltage without load.
3. Turn on heater or AC to MAX along with turning on highbeam headlamps. Increase RPMs to 2000 RPM. Voltage should be a minimum of 0.5 volts above your standing battery voltage. This is your charging voltage with load.
My numbers were 13.30, 14.01 and 13.85 when I replaced my alternator the last go around. Still going and going and ...
In your case I would add turning on stereo(max) to step 3 and see what the voltage level is.
Besides the alternator and battery, bad grounds and battery terminals are major causes for charging system problems. Loose and otherwise inefficient connections will cause the charging system to work harder, unnoticed, 'till either the alternator, internal regulator or battery have finally been taxed out.
If you get a 'Check Charging System' warning, and think you fixed it by tightening up a battery terminal - be wary... the charging system has been working doubletime for an undetermined amount of time to compensate for this. It would not be suprising to replace a major component in a short period of time following.
Did you know?
From the manual - the 'Check Charging System' warning will only be displayed when the voltage is between 8 and 9 volts or 18 to 21 volts. Below 8 volts or over 21 volts there will be no display. Normal(as far as the message center is concerned) is considered to be between 9 volts and 18 volts! Let me tell you something, the charging system is far from normal long before it gets down to 9 volts and way before it gets up to 18 volts. Rounding to whole numbers, 12 volts to 15 volts is normal, under 12 or over 15 is definitely trouble.
2002 Ford F-250 Super-Duty Powerstroke Diesel Pickup
2000 Mercury Sable LS Premium
1993 Lincoln Mark VIII
1991 Lincoln Mark VII LSC