Brian that's what I figured, but without asking I couldn't be sure
From Pilot DAR
The gearbox design, included a block of wax within, which would melt at a suitably high temperature after oil loss for whatever reason. Cast into the wax were spring loaded electrical contacts, which closed once the wax melted. The closed contacts told the pilot that the gearbox was now being lubricated by the wax, and down would be good.