Yes, which is why even after 15 years and still not remembering to switch
the manual switch off when going down to 2nd or 1st, I devised a lockout
circuit. This locks out the OD preventing it operating even in 3rd or 4th,
if one moves from an OD gear to a non-OD gear, until one moves the manual
switch off and on again. This does have a light, but that warns it is
locked out, not in an OD gear. See
http://www.mgb-stuff.org.uk/wn_gearsframe.htm and click on 'Overdrive
Having the OD engage just after one has gone into 3rd isn't harmful,
although it is rarely a good ration to be in so one gets the thump when
switching it back out again as well as the unexpected thump when it cut in.
----- Original Message -----
> ... if I leave the gear shift OD switch in the "On" position will
> the transmission try to go to OD as soon as I shift from second to third?