You need to get a volt meter to test the system.
key off engine off
Check battery voltage
Lets say it is 12.5volts
(under 12volts means bad battery)
On the back of alternator is a larger Black/Orange stripe wire, it may have a cap on it, remove cap and test for 12.5volts there, if no volts then a Fusible Link is blown.
There will be a 3 wire connector on alternator, unplug it, there will be a Yellow/white stripe wire on this connector, test it for 12.5volts, if no volts then a different fusible link is blown.
If Battery light is working then the green wire is OK
Check white wire that loops back to alternator to make sure wire isn't loose or broken at either end, this wire is not there on some newer alternators, it is internal.
If you have battery voltage at the above 2 wires(Black/orange and Yellow/white) and battery light is working then alternator is bad, period.
Flickering or dimming head lights at idle means at least one of the 3 fields in the alternator has failed, so alternator can't output engine voltage at idle RPMs, if you raise RPMs and lights work fine again that confirms a bad field.
Old alternator could have blown a fusible link when failing, which is why you need to test the wires.
A Fusible Link is a short wire that acts like a "slow blow" fuse, if there is a short the wire will heat up and separate without melting and causing a fire, these are used on alternators because there can be short high amp spikes in voltage that would blow a regular fuse instantly, the Fusible link won't blow just heat up then cool down after the spike.
Last edited by RonD; 12-06-2015 at 10:55 AM.