2000 Ranger Alternator?

[jefflos68]

My son has a 2000 Ranger, 4 liter. He was driving when the voltmeter gauge suddenly dropped to low, and he stopped to check it out. The connections seemed fine but it wouldn't start without a boost. We got it home, charged the battery and cleaned the posts and connectors. When we started the vehicle the voltmeter started normal but steadily dropped. My question is while it seems like the alternator, is there anything else we should be checking before we replace the alternator? Thanks for any advice.

 

[McCormack]

Some auto parts stores have battery load testers and alternator testers and they'll test your stuff for free.

 

[tmwalsh]

Using the parts store tester is a good idea. I would add that you should also check the condition of the battery. If it has a shorted cell, it can get low voltage quickly, and be unable to crank the engine. It can also damage the alternator by overloading the output. I have read that 'todays' alternators are not designed to re-charge a discharged battery, but cannot say why.
If you use a VOM or DVOM, you can check the real voltage at the battery posts, and at the output terminal of the alternator(large wire). It should be in the 12.5-7 range at rest, and go to the 14.x range with the engine running.
If you have an internal regulator, it may be replaced w/o replacing the whole alternator in some cases. An external regulator can be replaced independent of the alternator.
tom