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 new favorite website,
ZR-2 USA, and discovered RancherMatt's train horn 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 like
this one 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
sound 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
right-sized application 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.

Next question: where to put the compressor. Again, Viair makes a nice little
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
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 seller.
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 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"

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
  9. Teflon pipe thread tape.
  10. 3/8" nylon tubing (to extend the air intake line on the
  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
  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.
All the accessories to make everything work.
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 frame. I
also had to modify the air intake on each horn to get
another 1/2" of clearance between the radiator and the

Let's get started!
2004 Chevy Blazer ZR2
Onboard Air!
March 2007
Click on pictures for full-size view