If you have ever wondered why the stop light circuit wiring passes through the main lighting switch on the dashboard it is to control stop light use when blackout lighting is in operation. In the first BO position the 'dogs tooth' marker lights operate at the front and rear of the jeep. In the second position the BO headlamp also operates. In either BO position the normal stop lights are disabled and, if still fitted, a BO stop lamp operates instead.

M201s all left the factory with BO stop lights, even the later 24volt models. There is clear evidence for this in the circuit diagrams drawn at the time. On the left at the rear was a standard light unit with red lens, on the right a BO light unit with BO marker and stop light lens. These were later converted to standard light units rather than being replaced with new ones.

The conversion was not a particularly tidy one (see above left) and involved cutting the recessed section out and replacing the lens. Some light units have been converted in a very professional way, others look as though they have been butchered. It is possible that this reflects the difference between conversion at La Maltournee and smaller regional workshops.

Exactly when the conversions to dual rear stop lights began is not clear but it was certainly required as part of the addition of indicators for some jeeps from 1967 onwards. Initially the BO stop light facility was retained by adding a supplementary unit. According to technical bulletin BT 0631 this was to be mounted on the left side below the rear cross member, however, I have also observed many examples where the additional unit is fitted on the same side as the original on the right. It would appear that individual workshops had their own ideas as to which side it should be on.

The supplementary units came in a range of types made by different manufacturers with various bracket arrangements. The unit illustrated was manufactured by Gabriel Lyon. A large number of M201s also exist where the additional BO stop lamp unit is missing or there is no evidence that it was ever fitted even though the RH rear lamp unit was converted. This is a bit of a mystery in that it is possible that some regiments considered it unnecessary even though the concept of BO stop lights clearly did not become obsolete. I say this because the very late high visibility rear lamp clusters fitted to some M201s and trailers during the 90s include a BO stop lamp feature (see high visibility lights).