Frigid Chicago winters, combined with too much time on the Internet,
are a dangerous combination. What might seem like ridiculous
thoughts in the glory days of summer turn into completely reasonable
ideas when the temperature outside reads 4 degrees Fahrenheit.
Such was the case one January day when I visited my favorite
now defunct)
website, ZR-2 USA, and discovered RancherMatt's train
setup. RancherMatt is a dude from Upstate New York with a
penchant for ear-splitting blasts from the innards of his 2002 Chevy
S-10 ZR-2. While his post made me
think this might be a necessary
modification for my Blazer, the videos on made me
know I had to have the horns.

HB4H's are not just any horns. Know what
sound a locomotive makes before a railroad crossing? These are the
horns. They are powered by air pressure, which means their operation
requires an air tank and an air compressor. Bouncing cars have been
powered by air pressure for many years, which means plenty of tanks
and compressors are available for all types of auto applications. It's
just a matter of finding the right combination to power a set of
unnecessarily loud horns.

Air tanks come in all shapes and sizes. I wanted at least 2 gallons,
which is probably about the minimum for running a 4-horn set if you
want any type of sustained blast. Auto-application compressors come
in two general types: electric and engine-driven. Electric compressors
seem to be the most common due to their size (tiny) and price
(reasonable). Engine-driven compressors are mounted in line with the
same serpentine belt that drives the alternator, air conditioner
compressor, and water pump. They cost more and put additional load
on the engine but produce large amounts of air - enough to power air
tools. I decided to go with an electric compressor mainly because I
didn't see myself needing huge air volumes and the compact size
would be good for squeezing into small spaces. As with my
project a few years ago
, I wanted to preserve all possible interior
space, keep expensive modifications out of sight, and mount that
noisy compressor as far from earshot as possible.

So, first things first. RancherMatt had already demonstrated that the 4-horn setup could be squeezed between the
radiator and the grill of a ZR-2. But where to put the air tank and
compressor? RancherMatt mounted his inside the bed of his S-10; I
had other ideas. Could the tank and compressor be mounted under
the BlaZeR2? The short answer was yes, depending on the size of
the tank. Here's what I had to work with:
Tank dimensions are 23.5" long, 7.5"
tall and 6" wide.
This area is on the drivers side, opposite
the muffler (we're looking toward the rear
of the vehicle). It doesn't seem like much,
but there's a solid 2 feet of space from
front to rear and another 15 inches or so
in width. My goal was to find a tank that
wouldn't extend below the frame rail, so
my options were somewhat limited.
Fortunately, Viair had the
for this space, a 2.5 gallon
tank with six 1/4-inch ports. Mounted on its side, the tank is no taller
than the frame rail. Perfect.

Next question: where to put the compressor. Again, Viair makes a nice
100% duty compressor that is so small it almost looks like a toy.
Moisture resistance and horizontal mounting capabilities were an
added bonus.

Ahhh, my master plan was falling into place. On went the computer,
out came the credit card, and 10 days later I had a lot of cool stuff.
Now here's where it's a clear advantage to be the son of a farmer:
heated tool shed, heaps of scrap iron, every tool known to man, and
an advisor (Dad) willing to help keep me from destroying stuff
(including myself). To do this job, at minimum you
must have a drill
press and some sort of metal cutting device that doesn't involve a $15
hacksaw. Anything less will frustrate you beyond belief (an air grinder
works pretty well, too).

Both and
Thorbros (formerly Suicide Doors) sell
various HB4B four-horn packages complete with compressor and tank,
but none had the exact combination I needed. The horns and Viair
380C compressor came from Suicide Doors (now ThorBros), along
with a
Viair 110/150 pressure switch. I'll get to the installation
schematics later, but the pressure switch tells the compressor to kick
on when the air tank pressure drops below 110 PSI and to shut off
when tank pressure reaches 150 PSI. The tank came from an eBay
Let's see what's inside....
Viair 380C compressor, complete with
relay and intake hose and filter. The
relay is unnecessary if you buy the
Viair pressure switch, which has its
own relay inside. The air line is for
the compressor intake.
Four horns, 20 feet of 5/16" air line,
solenoid air valve and fittings
So now, the fun begins. The first
task is understanding what has to
happen to make these bad boys
start scaring the pee out of
unsuspecting individuals. For me,
it would start with a push button to
activate the solenoid that releases
the compressed air into the horns.
I didn't want the Blazer's horn to
activate the solenoid because I
don't feel like it gives me enough
control - the auto horn is activated
by pushing on the center of the
steering wheel in no specific spot.
With a separate button, I would
always know exactly what (and
where) to push.

When the horns sound for any
length of time, pressure in the 2.5
gallon air tank drops quickly, so
the air compressor will probably
need to start compressing. That's
where the pressure switch comes
into play. It serves two purposes:
a) senses when the air tank
pressure drops below 110 PSI;
and b) tells the air compressor to
switch on. Thus, the pressure
switch needs to be connected to
the air tank to sense the air
pressure, and also connected in
line with the main power wire
going to the compressor (power is
sourced directly from the battery).
Inside the pressure switch is a
relay which opens when the
switch tells it to, sending power to
the compressor until the switch
senses 150 PSI in the air tank.

The pressure switch needs its own
All the accessories to make everything
Removing the grille: 10 metal tabs...
...and two light bulbs. That's it.
Where'd that plastic come from?
For 10 minutes I tried to get the plastic
thingy out in one piece. Then Mr. Air
Cutoff Tool showed up.
Much better.
Now we're ready to get started.
What I was left with was the hood
latch frame in the center and a
metal line that I believe goes to
the power steering pump. The
horns must be mounted around
these obstacles, which is
perfectly doable as long they're
positioned in locations that also
avoid the grille. You'll see later
on, there's a small amount of
metal which must be shaved off
the right side of the hood latch
2004 Chevy Blazer ZR2
Onboard Air!
March 2007
power source to work. This source can be from just about anything
that's only giving it juice when the ignition is on. This serves as
protection from the compressor kicking on when the vehicle isn't
running and draining the battery. If the pressure switch isn't able to
sense anything, it can't turn on the compressor. I went a step further
and added an interior switch that would disable the horns altogether.

Connecting all of the components is a plastic-type air hose. The
Hornblasters kit includes an odd-sized 5/16" outside diameter hose
that is hard to locate elsewhere. Finding more of this line takes some
heavy searching. An alternative would have been to use a more
standard sized line such as 3/8", with separate 3/8" fittings.

Getting Started
For my setup, here's what I bought in addition to the horn kit, air tank
and compressor:

  1. Primary wire for the compressor - I used 10-gauge; enough to
    handle the compressor's 16-amp load.
  2. In-line fuse for the compressor - I used a fused distribution block,
    which combined the compressor's 40-amp fuse with the fuses for
    my main amp and subwoofer amp.
  3. Miscellaneous smaller-gauge wire for the pressure switch, push
    button and horn disabling switch.
  4. 12v push button.
  5. 12v switch for disabling horns.
  6. Small-amp in line fuses and holders for the pressure switch lead
    wire and the horn disabling switch.
  7. Miscellaneous wire terminal connectors.
  8. Grommet for wires routed through firewall and inside the cab.
  9. Teflon pipe thread tape.
  10. 3/8" nylon tubing (to extend the air intake line on the compressor).
  11. 5/16" tube-to-1/8 inch pipe T-fitting (for pressure switch).
  12. Pair of 5/16" tube to 1/4-inch pipe connectors.
  13. Drain cock for air tank (1/4").
  14. 175 PSI pressure release for air tank (1/4").
  15. Plugs for excess ports in air tank (1/4").
  16. Two 48" lengths of 1" x 1/16" steel (approximate width/thickness).
  17. Various nuts, bolts and washers, including machine and sheet
    metal bolts.
  18. Electrical tape.
  19. Zip ties and duct tape - man's best friends.

The first task is removing the grille, which is as easy as grabbing it in a
few key areas and giving it a sharp tug. Metal tabs secure the grille to
the frame, making for easy removal and installation. This is good,
because I removed and installed the grille approximately 132 times.
Even the turn signal light bulbs are easy to remove - a quarter turn
and they pop right out.

After the grille came off, an angular-shaped plastic piece, a trademark
of these vehicles, was visible behind the license plate holder. I
presume it is some sort of splash/debris guard to keep the radiator
somewhat clean, but I had to pull it out to have any hope of mounting
4 horns behind the grille. After carefully prying out some plastic rivets
and struggling with it like a Chinese puzzle box, I gave up and cut up
the plastic into pieces.
frame. I also had to modify the air intake on each horn to get another
1/2" of clearance between the radiator and the grille.

Let's get started!