2 ext power sources one pot

I have a stepper motor and two servos set as a knob for a robotic arm. I have 12v ext power for the stepper hooked to the arduino Jack. I want to hook the servos to a 4.5v breadboard Jack. The question is...

Can i hook the stepper and servo potentiometers to the 4.5v power source? Would that conflict with the stepper 12v hooked into the arduino Jack? Basically I want simplify the design by just using one power source for the pots. I just don't know if it is wise.

Supplemental: I just tried it with negative results, it seems i can only plug the 4.5v into the arduino Jack to make it work. That defeats my mission. I need to power the servos completely seperately from the stepper. Do I need a motor drive or something similar?

"A picture is worth a thousand words" Please show us how you connect all the staff, and please read this http://forum.arduino.cc/index.php/topic,148850.0.html

I figured it out. Rookie mistake. Didn't hook up to common ground.