This mod links the OEM (or aftermarket) horn to the OEM alarm to supplement the OEM siren with the added sound of a pulsing horn.

This mod will make the horn honk in sync with the flashing hazards when the alarm is tripped.  The horn will not honk with the hazards when they flash normally (i.e.,  when the alarm is activated/deactivated or when the hazards are switched on normally).

Materials:

·        Two automotive relays.  They can be SPDT (five-terminal) or SPST (four-terminal) rated. Expect to pay $3-5 each at radio shack or any auto parts store.

·        Several feet of 16-20 gauge wire.

·        Solder and solder gun, or a quality crimp tool and insulated crimp spade terminals.

·        Read the DIY "Tapping into the ETACS" for tips and general guidelines to splicing wires.

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Procedure:

Step 1:  Find the following four connectors and wires for splicing into:

·        ETACS connector C pin 8, green wire (hazards ground output)

·        ETACS connector C pin 9, green/orange wire (siren ground output)

·        ETACS connector A pin 1, red wire (power)

·        EM03 pin 13 red (horn output)

The ETACS is found behind the HVAC controls.  Connector EM03 is in a cluster of three connectors behind the fuse box.  You may need a flashlight to find them.  The ETACS connectors and connector EM03 are shown below.

Connector EM03:

Step 2:  Wire up the two relays as follows.  To make it easier, use the color-coded schematic below.  All standard relays have four or five terminals which are marked with the numbers 85, 86, 30, 87, and 87a (87a is only found on SPDT relays;  SPST relays do not have this 5th terminal, and it is not needed for this mod).

Relay 1 terminal 85:  hook up to ETACS connector C terminal 9 green/orange

Relay 1 terminal 86:  hook up to ETACS connector A terminal 1 red AND to Relay 2 terminal 86

Relay 1 terminal 30:  hook up to ground

Relay 1 terminal 87:  hook up to Relay 2 terminal 85

Relay 1 terminal 87a:  not used

Relay 2 terminal 85:  hook up to ETACS connector C terminal 8 green

Relay 2 terminal 30:  hook up to  ETACS connector C terminal 9 green/orange

Relay 2 terminal 87:  hook up to EM03 terminal 13 red

Relay 2 terminal 87a:  not used

NOTE:  If you would like to replace the siren sound with the horn (instead of supplement it as this mod describes), just cut the ETACS connector C pin 9 wire between the ETACS and the siren after you wire the relay into it.  This wire normally goes to the siren from the ETACS.  By cutting it and then running a wire from relay #1 to pin 9, the siren signal will only go into relay #1 from the ETACS, making the pulsing horn the only audible alert when the alarm is tripped. 

Enjoy!

- southpawboston