They were an accessory/option available for 1939 Chevrolet trucks, sold at the dealerships. They were not referred to as turn signals, but as directional signals. Here are the GM part numbers:
985257 (Pair, Rear with Switch)
985258 (Pair, Front Single Lens)
985259 (Pair, Front Double Lens)
Description:
GM Direction Signals consist of specially designed signal lamps, which can be mounted either on the rear of a truck or on the front fenders, and a control switch which mounts upon the steering column.
Selling Points:
As another step to "Safety" some states have made direction signals compulsory on trucks where the hand signal cannot be seen from the rear. The signal lens is of special design having circular prisms on the inner surface to collect the rays of light from the bulb and concentrate them into the beam. This provides a brightly lighted direction arrow which is legible from a considerable distance in daytime as well as at night. The switch assembly is of special design which mounts upon the steering column within easy reach of the driver. They are easy to operate and positive in results. Stress safety when selling direction signals.
Would probably have been the same for 1939-46, not sure.
Rick
