Per Installation Manual:
Horn Ring.
In order to utilize the horn ring control
of siren tones (Tap II) and other features of the siren,
the following procedure must be performed.
a. Locate the wire that connects the
vehicle horn ring switch to the horn or horn relay.
Cut this wire.
b. See figure 3-5. Splice the white/
yellow power cable wire to the horn ring side of
the wire that was cut in step a. Insulate the splice
with the wire nuts (supplied).
*************************************
> The horn ring transfer circuit of the siren is
> capable of switching a maximum of 2-amperes.
> Some vehicles do not have a horn relay and,
> consequently, will draw more than 2-amperes
> when the vehicle horn is activated. Consult
> your vehicle service manual or a qualified
> mechanic to determine the current required
> to activate the horn. If it is less than
> 2-amperes, perform the procedure in step c.
> If it is greater than 2-amperes, perform
> steps d through j.
*************************************
c. Splice the white power cable wire
to the horn side of the cut wire. Insulate the splice
with a wire nut.
d. Obtain a SPST relay of sufficient
contact current capacity to activate the vehicle horn.
Refer to figure 3-5 while performing the following
steps.
e. Mount the relay in a suitable
location.
f. Connect the horn side of the wire
cut in step a to the relay contact terminal.
g. Determine the “sense” of the
vehicle’s horn ring activation circuit, i.e., does the
horn circuit require a switched positive voltage or
switched ground for activation.
h. Connect the switched relay
contact terminal to the positive or negative potential
determined in step g.
i. Connect the white power cable
wire to one end of the relay coil.
j. Connect the other end of the relay
coil to the opposite potential of that connected to the
switched relay contact terminal in step h.