Typically would have been used to turn on an extra fuel injector or as an input to a boost controller or something of that nature. Saw a lot of this kind of stuff in the early 90's, Like turbotre said you should trace the wires down and find out what is doing. Many old things like this can cause you grief if they are still hooked up to something and I like to remove any thing that could be an electrical hazard. Let us know what you find.