'48 starter question

[Trekster]

I have 2 '48 2 ton trucks that I (someday) will combine into one truck. I removed this starter from one of them and have never seen one like it. The relay looking thing has three terminals. One of the wires goes to the coil and the other two attach to each side of the distributor. When the starter pedal is pushed, the transfer bar moves a lever on the relay and it makes an audible click. My guess is it enables the truck to be started without a key but I am not sure how to turn the engine off. I could be way off also. Does anyone known what this is and what it does?

Thanks