I have added an exhaust fan in bathroom to an existing single light switch that operates one light. I'd like the switch to turn the light and the fan on together. The existing switch has one feed of 14-2. I ran a second new 14-2 from the switch box to the new fan and hooked up to the switch. When switch was on, the light came on but not the fan. When the switch was off the light went off but the fan came on. I'm wondering if I should have run my new wire from the light's wiring to the fan instead of from the light switch?
You should extend the wiring from the light, not the switch. There should be two wires on your light fixture, one grounded (neutral), and one ungrounded (hot) conductor that's controlled by the switch. Extend those wires to the fan, along with a grounding conductor. That will allow the switch to control both the light, and the fan simultaneously.