Chev CMP starter question

[RichCam]

Maybe this is a Chev CMP trivia question.....

I was looking closely at the rear of my C-15A Wire 5 truck chassis and I noticed that on the DS rear of the frame, just behind the axle and just in front of the rear leaf spring mount, that there is a push button contactor (3 wire) mounted onto the frame. The push button contactor looks very similar to the push button "starter" that is mounted on the dash. The rear frame contactor doesn't have any wires connected to it so I don't know where they go. There isn't a reference to this contactor in the maintenance or parts manual that I can see.

What is it for? I see a similar mount hole on the Chev C-8A frame and the C-60X frame as well. Not on the Ford frames though.

I look forward to your comments. Thanks!