Just follow the top rad hose. It's in the housing.
The thermostat is located on the front of the engine under the elbow at the end of the radiator hose
You most definately unpluged the sensor wire. It's a single red wired that plugs onto a sensor just passed the thermostat.
Check the engine end of the upper radiator hose
installer.com
The fuel filter on a 1990 Mercury Topaz is typically located along the fuel line, mounted on the chassis beneath the vehicle. It is often found near the fuel tank or along the frame rail, making it accessible for replacement. Always refer to the vehicle's service manual for the exact location and detailed instructions.
The daytime running light module on a 1990 Ford Mercury Topaz is typically located near the driver's side of the engine compartment, often mounted on or near the firewall. It can also be found in the fuse box area or behind the dashboard, depending on the specific wiring and configuration of the vehicle. For precise location, consulting the vehicle's service manual is advisable.
5 W 30 on a 2.3 Liter.
you can see that in www.tempotopaz.com and many other things about it
on autozone .com on autozone .com on autozone .com
YES Some were all wheel drive. Allthough both front & rear are limited slip, & the rear only if the front wheels are spinning.
BIG JOB Get a manual on your car from the parts store and it wil have pictures .
The thermostat housing is located at the engine end of the lower radiator hose.