We are unable to locate the Petcock on our 1999 Oldsmobile Cutlass GL. We have jacked the car up and looked on the lower right and left hand side of the radiator with no success. Please help. Visual schematics would be helpful too! Thank you.

Well the only petcock that comes to mind is the radiator drain petcock. It would be located in the bottom of the radiator plastic tank, at either the right or left end on the engine side. Many times the tabs that you use to turn it with are broken off, making it harder to see where it is. If you are going to do a coolant flush, just disconnect the lower radiator hose to drain the coolant; it is faster!
If this is what you are doing there is a vent screw in the top of the thermostat housing to let out air when filling the system. VERY IMPORTANT TO DO. I hope that this answers your question.

Fuses are located in the relay center, on the passenger's side, below the instrument panel. You must remove the sound insulator on the right side of the passenger footwell to replace these fuses. Open this and you will see a bunch of relays and in the lower left hand corner is 4 rows of 3 fuses. The 3rd one down on the left hand side is the horn.

It is located right next to the blower motor.

On 1980 and later models, both the turn signal flasher and the hazard flasher are located at the lower left hand and the upper right hand corners of the fuse block respectively. Remove these by pulling them from their connectors.
The lower dash panel may have to be removed to gain access to the unit.

in fuse box or under hood,it is round https://www.bing.com/images/search?q=1999+oldsmobile+cutlass+flasher+location&view=detailv2&qpvt=1999+oldsmobile+cutlass+flasher+location&id=1F46E2CC2D43F586083EB232E2DD5B0B5EEAB9A6&selectedindex=7&ccid=E0ipuhW%2B&simid=608012729444401682&thid=JN.voUt6aRy%2Fjo0AbcnYGtIJA&mode=overlay&first=1

It will be in the fuse panel located Drivers Side Lower Dash behind access Panel,or Drivers Side just under Dash!

Replacement The turn signal flasher is located under the dash either to the left or right of the steering column on most models. The lower dash panel may have to be removed to gain access to the unit. The hazard flasher is located in the fuse block.On 1980 and later models, both the turn signal flasher and the hazard flasher are located at the lower left hand and the upper right hand corners of the fuse block respectively. Remove these by pulling them from their connectors.

It depends on what motor you have...But the locations are....on the lower side front of the motor... Or on the back side of the motor, in a tight space, you may need a flashlight...Or if you look on the passenger side, right in between your lower control arm...where your right front tire is located, you may find it there...Goodluck...

Most are difficult to get to and so many don't work correctly that it it's almost silly to even use it. Far easier is to simply remove lower hose from radiator. It works better and faster. Just be careful though...Don't do hot or you may get an unwanted scalding bath!!

follow the upper radiator hose to the motor and you will find the thermostat housing there