Check the output at the alternator itself. Put your multimeter on the output post that has the wires on it. If that isn't showing 14V or close to it at idle it is a dud alternator. If it is showing a high voltage check the reading on the + battery cable terminal & then on the + battery post itself.

 

If you have an external voltage regulator, start the engine and connect a voltmeter to the battery + and - terminals. Remove the plug from the regulator and connect a jumper wire to the plug between the A+ and F pins and note the voltmeter reading. If it doesn't move you have a bad alternator. If it increases you have a bad voltage regulator. Do not connect the jumper for more than 10 seconds at a time within a minute or two of each other to avoid overheating the alternator. The output at fast idle with the headlights on should be no less than 14.5 volts.

PS: Unless you want to risk damaging your alternators rectifier bridge, do not disconnect the battery while the engine is running. This is an old generator test and not suitable for alternators.

 

ok ill check today. if alternator is good then what? ive heard it can do this if a fuse is blown but my dad did the wire harness and i dont know how to check if there is or noot.