1994 dodge 2500 12v lights and battery gauge
 

All Lights r very dim
Battery gauge in dash showing 11 to 12 volts all the time
2nd new 160 amp alternator and two new batteries
With motor running testing at battery and at alternator showing low voltage like motor is not running

Any ideas anyone

What is the voltage when testing at the alt. And battery?

10 or so volts

Check for battery voltage at the Alternator field wire gray/wht. if no voltage proceed below.
Check the ASD relay in the power distribution box (swap with a simmilar one in the box). Check voltage on pins in the Power distribution box and the 30 amp fuse # 4.
Below is a diagram to help find the problem.

Attachment 30688