[TR] O/D safety switch

[Randall]

> this allows only using O/D in 4th 
> gear.. better than nothing I guess..

Just a SWAG, but the GT6 used the D-type OD which was marginal even behind the much smaller Spitfire motor.  My _guess_ is that they
limited it to 4th gear because the OD could not handle the engine torque multiplied by the 3rd gear ratio.

I don't know how the ratios work out on the GT6, but on the TR2-6, 3rd OD is so close to 4th direct that it's almost not a separate
gear.  That's not to say 3rd OD is totally useless, but it's also not a big loss, IMO.

Randall