On this 94 GC, with everything off reads at 14 vdc. Sitting at idle, "Parked". turn on the head lights, it drops to about 10-12vdc ad lower if I follow it up with the a/c, rear defroster, ect. Should I be looking to replace the alternator? Once I bring up the RPM's(1000-1500) everything comes up brighter and the voltage reads about 14vdc.

I would first make an idle adjustment. Make sure it isn't dropping below around 750 at idle. Any car will show a drop in voltage if the idle is set too low.

I would first make an idle adjustment. Make sure it isn't dropping below around 750 at idle. Any car will show a drop in voltage if the idle is set too low.

How can one adjust the idle on this car? I thought it is controlled by the IAC which is automatically set by engine management, isn't it?

The IAC (depending on the style you have), can be slightly adjusted when removed by turning it in clockwise. This reduces the extension on the plunger allowing a little more air through at idle. Be VERY careful not to force it. It may just need to have the carbon buildup cleaned off too, both at IAC and throttle body bore.