GEN light came on this morning, after drving for about 15 miles.
First time ive seen it in about 5 years. once i noticed it, i looked volatage guage was hanging pretty low.

is this just the alternator going?

 

That's the most common , the regulator is in the ECM , but also check connections , battery pos + grnds , fusible links , fuses .
need to test the alt directly , the 2 small wires on back of alt are for control of alt , disconnect both , then jumper one to ground & other to battery , but only for about 30-60 seconds , this is what the regulator does , it turns on the electrical field to the alt , making charge at max - this is why just for a minute or less , because if the alternator is working it can run too hot .
If it works then you need to find out why not , does the tack read RPMs , this is one of the things the computer uses , the crank sensor .

 

everything else was working fine, tach, all controls, heat, radio.
Just came on out of nowhere, when i go to lunch ill look again, if its like last time, the symptom will be gone.

 

One of the common things when the alt quits is the brush's .
There's a couple ways to go , rebuild your self or get new .
This is where I go .

http://www.fostertruck.com/dodge/default.htm