I believe it is in the left front (driver's side) fender, I had to pull the wheel and remove the wheel well cover to get to mine. (2000 Taurus sedan).
Answer.
Taken directly from the service...
P1506 IAC OVERSPEED This code denotes that the IAC is causing the motor to have an excessively high idle. This maybe caused by a vacuum leak, the IAC being unplugged or the wiring compromised, the...