sorry, should have mentioned that the bike is a 2008 model with airbag. Got the bike new in Sept 09, have 4500 miles on it and the grip problem (left only heating up with only passenger seat heater activated) has been there since new, maybe. Thank you for your comments.
Being miswired is unlikely but not impossible. The manual unfortunately doesn't show where the wires run in the harness, just where the terminate so it will take some work with a meter to find the problem.
See if the big wiring connector under the seat is full connected.(i also think ,that Honda recommend to relocate this connector a bit , but cant remember the details ).
This sounds like a ground problem to me !