Part 1: Mounting the Horns
The Hornblasters.com set comes with 4 horns tuned for different
pitches, much like train locomotive horns. The pitch of a horn is
determined by its length - in this case, the longest  horn is the lowest
pitch and the shortest horn is the highest. Sizes range from 12 inches
to 20 inches.

For a Chevy Blazer, the most effective mounting location is behind the
grille, which assumes you want them concealed. You can always
mount them on the roof rack but what fun is that? The element of
surprise will be key to your enjoyment of these horns - you don't want
to give yourself away by mounting the horns in a clearly visible
location now, do you? Didn't think so. Pickup truck guys have the
option of mounting their horns under the bed, but the 2-door,
short-wheelbase Blazers just don't have enough room if you want to
conceal the air tank and compressor underneath, as I did (more on
that later).

So get ready for the trial-and-error method of mounting the horns.

Minor Horn Modification
The first task at hand is to modify the air intake of each horn. The
intake is a 1/4" NPT male connector which is about 1/2" longer than it
needs to be, so I trimmed it down. This modification became
immediately necessary when I mocked up the first horn bracket and
tried to push the grille back on. Once the 90-degree female connector
goes on the end (adding another 3/4" to the total length), it pushes all
the way up against the radiator and still makes the horn stick out too
far to get the grille fitted properly.

The trim job solved this, although a thread repair tool or NPT die
would have been very handy. After the trimming, the 90-degree female
connector wouldn't thread back on. I'd left my tap and die set at home
and couldn't find the right size die in my dad's stash of tools. Instead, I
un-threaded the entire intake connector and simply reversed it - the
cutoff end was threaded back inside the horn. The downside of this is
that the air intake thingie doesn't thread into the horn as tightly (it's
just a plastic housing) and I had to be careful when tightening the
support nut and the 90-degree connector (the whole thing wanted to
turn).

It really doesn't take more than about 3/4" of thread protruding from
the horn to make these fit on the mounting brackets I used. I left
enough space for the metal bracket that supports the horn (1/8" inch)
and for the support nut (with washer) that threads onto the air intake
on the other side of the bracket (another 1/8" or so).

Mounting Brackets
The horns are pointed downward, as recommended by
Hornblasters.com. This means metal brackets must be fabricated,
but it's fairly easy. I bought some 48" lengths of 1" wide (roughly)  
steel at Home Depot. The whole job could have been done with just
the one piece but I ended up using a bit of the second length of steel
because I re-cut one of the brackets. Each bracket spans the gap
from one side of the radiator to the middle support down the center.
To get access to the center support, the hood latch frame had to go
(three 13mm bolts - pretty easy). Once I had a general idea of where
each bracket needed to be, I marked where the bolt holes on each
end of the bracket would line up with the radiator supports. But to get
to that point, I had to also consider the mounting position of the other
ends of the horns.

Skid Plate Mounts
On the "horn" end of each horn is a bolt for securing to whatever it is
you'd like it fastened to. The later model ZR-2's came with a carbon
fiber skid plate with an inch-or-so lip that is perfect for connecting the
ends of each horn. In order to keep the skid plate  relatively painless
to remove after the horns were mounted, I cut a slot in the lip of the
plate for each horn-end bolt. The brackets secure the horns pretty well
by themselves; all the horn-end bolts need to do is keep the horns
from flopping side to side at their ends. A cutting tool was the key
here, but even more importantly, I needed to know the final mounting
location before cutting. You'll see later, I miscalculated slightly on one
of the horns and ended up with a horn that wasn't straight. Not that big
of a deal because everything still fit fine and nobody sees the horns
anyway, but it still bugs me a little.

Mock It Up
After playing around with various mounting positions, it became clear
that the longest two horns need to be on the outside and shorter ones
on the inside. In the pictures, you can see I positioned the 20" horn on
the left side, out of the way of the steering pump metal line. The short
horns fit pretty well next to the hood latch frame, with a small amount
of grinding (see photo). The smallest horn goes on the left side of the
frame (as looking straight at it; it's actually the passenger side). The
two mid-sized horns work well on the right side, in between the metal
lines. They can both be mounted on the same bracket, while the
horns on the left require separate brackets. This becomes more clear
as you see how the horn-ends need to fit into the skid plate.

As I experimented with various horn positions, I had to take into
account the shape of the grille. There are certain positions that work,
and others that don't. It's a trial and error game, simple as that. The
good news was the grille being so easy to take on and off. The
bumper stayed put, mostly because there was adequate clearance to
grind slots for the horn-end bolts and position the ends appropriately.

Final Mounting
Now, the moment of truth. All holes were drilled, bolts tightened,
connectors connected, and it all fit perfectly. I used a combination of
machine screws and nuts where possible, and sheet metal screws
for the rest. Drilling near the radiator was a bit of an adventure, one
that required a steady hand and a bit of patience. In the end, it doesn't
look like it should take that long, but it does - probably half my time on
the project was spent mocking up the horns.

Getting the Air to the Horns
Next up is attaching the air lines to the horns, and this is where 5/16"
outside diameter air line is a bit annoying. The Hornblasters.com kit
comes with 20 feet of line, which ended up being the perfect length of
hose for my application. But if you need more, plan on ordering it from
McMaster-Carr or similar sources because your local NAPA probably
won't have any. And if you want to do anything special like teeing off
the air line (as I did), you'll need extra 5/16" compression fittings.
These are also difficult to locate.

But if all you want is really loud horns, the Hornblasters.com kit has it
covered. An air line distributor takes the source of air and splits it into
four separate lines, each connected to a horn.  Compression fittings
link it all up. Each of the 4 lines should be the same length so that the
air will reach each horn at the same time and they all produce sound
at once. About 14 inches was just the right length for connecting the
horns furthest from the air line distributor, which I zip tied behind the
hood latch frame. The air line is nylon, which feels like plastic and
has a limited curve radius, so that must also be taken into
consideration with positioning the air distributor.

A solenoid-activated air valve activates the horns. The kit assumes
you'll use the existing auto horn to activate the solenoid. Presumably,
a wire is run from the auto horn and whenever you push on the center
of the steering wheel, the air horns make noise. I didn't want this,
mostly because the activation points on the steering wheel are less
than precise. I needed the kind of control a separate button provides.
Also, I wanted to preserve the auto horn for those occasions when I
only wanted to remind someone of something, like a green light or
turn arrow. The air horns would be reserved for acts of retardation on
the street or patterns of annoying behavior. Another consideration
was keyless entry - remember the sound that comes when you hit the
lock button on the key fob twice? That would be the horn. I didn't want
the train horns going off every time I locked my Blazer.

It is definitely simpler to use the auto horn to engage the air horns. A
separate horn button requires locating an ignition wire and running it
from the solenoid, through the firewall and into the cab to wherever
the button is mounted. And to do it right, I wanted a dash-mounted
button, which added more work. But oh, it is
so worth it.

I placed the air valve as close to the air line distributor as possible, as
recommended by Hornblasters.com. Since the compressor and air
tank would be mounted on the drivers side, I chose a valve mounting
location next to the drivers side headlight.

Now, let's
mount the air compressor and tank.....
That extra 1/2 inch was a lifesaver.
With the 90-degree fitting attached.
Duct tape and zip ties: man's best friend for mock-ups
Take a bite out of the hood latch frame and all is good.
Stupid crooked horn....
One line in, four lines out
14-inches times four
One of the most important little gadgets in the whole system.
Blue wire is power; brown wire is grounded to the frame. I had to
reverse the valve bracket to get the air output side of the valve to
point in the proper direction. The valve must be mounted upright,
as shown here.
The components of a compression fitting
Air line compressed, fitting tightened up and we're ready to go.
Onboard Air!