Voltage measurement not as expected on 3-way
Newbie learning about electricity.
I got a digital multimeter, and have been measuring various devices.
I have a pair of 3-way switches controlling the basement lights.
I measured voltages on one of the 3-way switches.
When the lights are off, I measure 120 volts between the 2 traveller terminals, which is what I expect to see.
With the lights on, I measure 80 volts between the travellers. I get 120 volts between the hot traveller and ground, and I get 13 volts between the other traveller and ground. I get 120 between the common and ground, and 120 between the common and non-hot traveller.
Why do I see only 80 between the travellers when the circuit is on?