123GT had a pair of pull switches under the edge of the driver's side dash. They are the same switches as used for the under dash light above the passenger side shelf. Ergo, use either or both. MGB, not factory so would be owners choice.
There are actually 3 choices of lamp, or were when these additions were common, fog for fitting low to get under the fog and light up the road edge, driving, for general extra light and to extend the range of the standard lights and spots for concentrated light for extra range. Spots OK for deer spotting but often failing to give extra light where you most need it. Set up any of these lights to give the best coverage for you and your style of motoring. Taking your spanners with you to a flat straight road on a very dark night is very worthwhile. Spots and driving lights should always be wired to switch off when you switch down to dipped beam. due to oncoming traffic. Beware, this can leave you instantly "in the dark" if your extra lights are very bright!