On my 98 Sable, it's up under the passenger side of the engine compartment - way towards the front.
Maybe the 2003 is still in the same neighborhood.
1999 mercury sable horn replacement
where is the horn relay on my 1993 Mercury Sable located
The horn relay for a 1998 Sable is on the back of the distribution block. The block is under the dash on the drivers side.
Narwhals
routing for serpentine belt 2003 mercury sable
The fuse for the horn of a 1995 Mercury Sable is located in the engine compartment fuse box. Fuses in the fuse box are labeled with numbers, the number direct what job they handle. The horn relay is in slot 12 and is rated at 20 amps.
on the steer wheel
Push in on the turn signal indicater
Grain De Sable was created on 2003-06-02.
The low pressure port for the 2003 sable is on the passenger side of the engine compartment. It is right at the firewall made into a hose.
36R
On a 2003 Mercury Sable : The thread on cap on the engine coolant reservoir is the 16 PSI pressure cap / radiator cap