how to pull a code/ 94 cavalier

Hello all, My 94 cavalier is setting a code that I can not get out of the system. 3.1 eng. All the auto parts stores have code readers, but they start at 1995/2006. The Haynes manual says you can jump a wire from the ground to the power, and the check engine light will tell you what code is being set. The manual does not say what leads are power or ground.

The plug under the dash has only 4 wires going to it: Orange, White, Black, Brown. I tried all combinations to find out which one was power, and ground. No luck. Any thoughts?

Thanks in advance,

RB6667