I think my alternator bit the dust. I have a voltmeter - how do I test the output on the alternator?

Battery light comes on, stays on, batt not charging.
1991 Explorer.

Thanks.

 

Red connector on Positive battery post
Black connector to Negative battery post

Set M/M on the 20V scale

With no accessories running(heater,Wipers,headlights) >

check voltage of battery should be 12v-13v

rev engine up watch for voltage increase to about 13.8-14.5 V

Now turn on one accessory one at a time and observe voltage and VReg kick in

If the voltage values stay up ,the alternator & V Reg. is fine


Dennis

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If you have an Advanced Auto or other good Auto Parts store nearby, they have computerized testers that can tell what individual PART is bad. Most'll do it for free, too.

 

take a pair of dikes and engine running and put on the back ball bearing plate of the alternator and check if its magnetized. If it is, usually means it put out juice or meter lead (-) to engine and other lead to (+) of the alternator. should read over 14 volts.

 

If you don't have a shop or store nearby to test for free, the suggestion made by "mil1ion" is the best one. The diodes in the alternator don't last forever. They fail usually one by one. Mine did that just recently. If one diode fails, you might not even know it, because it will still put out sufficient juice MOST of the time. After a second, or third fails, it will read good voltage when there is NO DRAIN AT ALL. But, as soon as you start turning on loads (heater, headlights, etc), the voltage drops, until it won't even charge the battery. If you have an external regulator, they are cheap. I'd replace it, even if you're not sure that it is the problem. It's one less thing that you'll have to worry about "down the road". Then, if no improvement, you can be pretty sure it's the alternator.