Fan Not Working A/c Fan Works Engine Hot Fan Does Not

I Have A 1994 Grand Prix Se With Dual Electric Fans. The A/c Fan Works Fine But The Engine Cooling Fan Does Not. I Jumped The Terminals At The Fan Relay And The Fan Turns On. The Relay Is Fine (swapped It With The A/c Fan Relay And It Operates As It Should). At The Terminals Of Relay I Found 12 Volts On Two Of The Pins (one To Trip The Relay And One To Go To The Fan). I Had Continuity To Ground On The Fan Side Of The Circuit As I Should But I Do Not Have The Signal Wire Sinking To Ground When The Engine Is Hot....and I Mean Hot.

Where Is The Coolant Sensor For The Fan On This Car?
Does The Signal Go Through The Engine Ecu First And Then To The Relay?
Please Advise