I have a 1992 Dodge 2500 diesel; the alternator gauge shows a normal charge. However when I apply the brake pedal, activate the turn signal, turn the head light dimmer switch or activate the horn the alternator gauge shows rapped discharge.

I applied a voltmeter on the battery before and during this discharge issue and the voltage remains the same to the battery. I have replaced the alternator, ECM and checked all electrical wires for shorts.

 

It's probably the main body ground. It's on the core support right in front of the battery, a lot of times the wire gets broken.