heater wire 120v 2-wire. one side ribbed and the other white writing?
The ribbed side is the neutral (actually called grounded conductor, not to be confused with the equipment grounding conductor). 

NEC 400.22 Grounded-Conductor Identification. One conductor of flexible cords that is intended to be used as a grounded circuit conductor shall have a continuous marker that readily distinguishes it from the other conductor or conductors. The identification shall consist of one of the methods indicated in 400.22(A) through (F).

(F)Surface Marking. One or more ridges, grooves, or white stripes located on the exterior of the cord so as to identify one conductor for cords having insulation on the individual conductors integral with the jacket.