Most likely under the hood of the car in the black fuse panel box. But first check your book that comes with the car to rule out the panel box under near drivers left knee.
On a 1999 Mercury Sable : Relay # 30 is the Powertrain Control Module ( PCM ) relay
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PCM stands for Powertrain Control Module on a Mercury Sable
The 1999 Mercury Sable computer module can be located behind the passenger side dashboard. The dashboard will need to be removed in order to view the computer module.
On a 2003 Mercury Sable : In the Power Distribution Box ( which is " live " ) located in the front of the engine compartment by the battery ( # 30 is the fuel pump relay ) Also , # 16 is a 20 amp mini fuse for the fuel pump relay
location for fuse, and relay switch on a Mercury Sable
The Central Control Relay Module (CCRM) in a 2000 Mercury Sable is typically located in the engine compartment. It is mounted on the passenger side, near the front of the vehicle, often close to the battery or fender area. This module controls various functions, including the fuel pump and cooling fan relay. Always refer to the vehicle's service manual for specific details and diagrams.
In the relay block with the other relays.
where is the horn relay on my 1993 Mercury Sable located
The headlight relay on a 1999 Mercury Sable is typically located in the power distribution box, which is found under the hood on the driver's side. You can identify the relay by referring to the diagram on the cover of the power distribution box, which labels the various components. If you're having trouble locating it, consulting the vehicle's service manual can provide more specific guidance.