Curious, HOW did you know the 120 side was on?????? There is NO indication of if on or off unless it does NOT heat. You stated something odd. You said you had 120 at the White but NOT the Black. Then stated you had 120 between the white and Black. That is at odds with the statement. You cannot have it both ways. Then you said you cannot access the Junction box or tstat without pulling the W/H. But you accessed the Element? IF you have a older Atwood, the the tstat and junction box AND the element are all at the rear. If you have a newer Atwood the tstat is on the outside and the 120 element and junction box are still at the rear. If you have a suburban, the tstats and the element are all easily accessed at the outside area. ONLY the 120 junction box is available if pulled. SO, what brand and model and year do you have? Doug