You can or someone else may have installed a push button start to use while working under the hood and left it there. Some a/c ports on lines look like buttons. But if you can add photo's please do and information on its location and what it is hooked up to.
If it's on the driver's side, bolted to the firewall, with orange, yellow, and green wires hooked up to it it's the starter/seatbelt interlock bypass button. Originally the engine could not be started unless you fastened your seatbelt. This button enabled you to bypass the system if it malfunctioned. By the later '70s it was legal to permanently bypass the system but the "fasten your seatbelt" light had to still come on when you shifted to drive. HTH. -Jim
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