I have a switch that controls a light as seen in this diagram. There is no neutral at the switch, instead, it picks that up from somewhere else. In the light receptacle it pigtails into the light and continues to the garage.
I measure 120v between the source hot and ground, and 120v when the switch is on between the hot lead and ground. In the light box, with the light disconnected I get 19v from neutral to ground. with or without the light, I get 90v between the hot to neutral.
In the garage, the outlets read out 120v and everything connected to them seem fine (work).
What is the right way to diagnose this? Any ideas why I'd be getting 20v in the neutral?