Here is a photo of a turn-signal switch on Pat Sheridan's 41-46 Chevrolet truck that is displayed on his 1946 Chevy Truck
Optional Equipment and Accessories
page. Send him an email message for information/documentation (Stovebolt name: Sheridan)?

I do not see a turn-signal unit in the 1941 or 1946 Truck Data Book but it still might have been available - maybe Pat has an accessory parts list?

Brad's '41 to '46 Chevies website is not working - he might also have documentation/information.