alternater question

[cooler1054]

my cj is not keeping a charge. I have 12 volts at the post on the alternater when running (to low I know), but when I take the wire off the back of the alternater and test I get 15 volts. What gives? I'm thinking bad alternater but it gives out the 15 volts when disconnected.

 

[DonnyG]

In most cases, the battery will act as a load. By removing the battery cable from the battery, you are allowing the alternator to produce a full load current. This is not good for the alternator. Using a meter, check the voltage at the battery (engine off). Then, start the engine and check the voltage at the battery again. If the voltage is the same or only minimally higher, and all wires to the alternator are connected, the alternator is bad.