Thanks guys!
PB, I did as requested and got the following using a 60hz tone and measuring between the outside & ground and middle lugs & ground for each set of wires:
Outside lugs:
Red - 1.570v
White - 1.572v
Inside lugs:
1/4 volume - white: 0.051v, red: 0.060v
1/2 volume - white: 0.178v, red: 0.187v
3/4 volume - white: 0.645v, red: 0.650v
Full volume - white: 1.572v, red: 1.570v
So it looks like up until the end, the right channel is slightly higher in voltage than the left, but it gradually drops as the volume is turned up.