Overdrive question

["M. E. Foster" <foster_m@swbell.net>]

If I drive with overdrive engaged for 15 minutes or more, a large voltage seems
to be building up between the transmission and the rest of the car so that if I
touch the steering wheel with my left hand while I shift out of 4th gear into
neutral with my right hand I get a very substantial shock. It only happens when
overdrive is engaged and only when shifting out of gear. Anyone know what's
wrong and what I can do about it? Thanks.