If I had to make a wild guess, the terminal with the different shape would be the battery.

Mike will this switch physically mount on your truck correctly.
1947-53 Chevrolet truck switches have ears for the mounting screws.
The one you have is for later model trucks.
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Ignition Switch GMC.jpg (85.58 KB, 96 downloads)

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."