found port but -
I finally found the OBDII connector on the 04 GMC. It was up under the headlight switch far to the left.
Anyway, diagnostic code was for the right front wheel speed sensor. I replaced the sensor and harness, re-checked and code is gone. Now the dash light "ABS" is still on - how can I turn it off? I thought since my Actron reads ABS codes it should be able to turn off the light - nope.