The only true way to determine the function of a wire or pin on a 7 way plug is to test it using a circuit tester like the Cordless Circuit Tester # PTW2979; unfortunately colors are not standard or a reliable way to determine function.
If you're going to be adding a new 7 way connector like the 7-Way Molded Trailer End # 54006-009 to your trailer, you'll want to connect each wire to a battery and ground to determine which function is activated when power is supplied. Once you're determined... view full answer...
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