Alternator excitement issue
 

Im having an issue with my alternator always being excited, the alternator is a truck style 4 pin unit. The factory wiring for the alternator has not been changed and the ecu controlls the alternator fine with no check codes.

I did a volt test and am getting 2.75 volts on the brown indicator light wire when the ignition is off, if I disconnect this wire the alternator is no longer excited. There is no voltage on the field duty cycle wire.

Help!

Well, it looks like you have an engine swapped Mazda, so I'm gonna guess that at least some of the wiring has been modded. The brown exciter wire needs to come from a "key-on" source, so check there first...