Kleinn TRX21-734 Ram TRX Train Horn & Onboard Air Kit Review

Methodology

This review aggregates publicly available information from manufacturer specifications, retailer listings, and verified user reviews. We do not perform hands-on testing. Last reviewed: October 26, 2026. Our primary sources are Kleinn’s official product page for the TRX21-734 kit plus Kleinn’s separate pages for the Demon Model 730 horns and the 6450RC compressor. We cross-checked the price and the air tank spec against a Desert Rat retail listing. Every external URL we relied on is listed in the Sources section at the end.

Quick verdict

The Kleinn TRX21-734 takes the formula Kleinn uses for its heavy-duty truck kits and applies it to the 2021-2024 Ram 1500 TRX. You get the flagship Demon 730 triple horns, the 200 PSI waterproof 6450RC compressor, 1/2-inch airline to the horns, and powder-coated brackets that bolt to factory mounting points, so nothing needs drilling, cutting, or welding. The price is $1,499.95, $100 below the RAM HD version. Kleinn says the spare tire stays in place, and on a TRX that matters. We rate it 4.2/5. We took points off because the 157.8 dB claim has no test distance, the kit page doesn’t list a tank size (we had to get it from a retailer), and the kit won’t fit TRXs with Mopar power steps. In our editorial opinion, it’s the cleanest way to put a real train horn and onboard air on a TRX without fabricating anything.

What it is

The TRX21-734 (Kleinn SKU KL TRX21-734) is a direct-fit train horn and onboard air package built only for the 2021-2024 Ram 1500 TRX. Kleinn sells it on a product page with variant options. The Model 730 Train Horn and Onboard Air System reviewed here costs $1,499.95. An Onboard Air System Without Horns (KL TRX21-OBA) costs $999.95. Unlike the RAM HD page, the TRX page doesn’t offer a cheaper Model 230 horn kit, so if you want horns on a TRX, the 730 kit is the only direct-fit choice.

Kleinn’s main pitch is the mounting. The brackets are laser-cut, powder-coated steel. They’re designed at Kleinn’s Tucson, Arizona facility and bolt to factory chassis points for what Kleinn calls a “no-drill OEM-style installation” with “clean, stealth, under-truck mounting.” That’s the difference between this kit and a universal kit like those covered on our Kleinn reviews hub.

Who it’s for: TRX owners who want the loudest horn Kleinn makes plus real onboard air for airing back up after the trail. The kit suits owners who’d rather pay for engineered brackets than give up the spare tire or fabricate mounts. If you drive a RAM 2500/3500 instead, see the RAMHD-734.

Specifications

Spec	Value
Part number	KL TRX21-734
Fitment	2021-2024 Ram 1500 TRX
Horns	Demon Model 730 triple train horns
Sound output	157.8 dB at 150 PSI (test distance not disclosed)
Horn construction	Spun steel trumpets with XCR 2.0 black coating; stainless steel and zinc alloy
Horn rack dimensions	22.5” L × 18.5” W × 7.25” H
Solenoid	Kleinn VX6003 brass
Airline to horns	1/2” Max-Flow
Compressor	Kleinn 6450RC, 200 PSI max, waterproof and fully submersible
Duty cycle	100% at 100 PSI
Compressor flow / draw	2.1 CFM at 0 PSI; 23 A max
Compressor dimensions	11.25” × 4” × 6.5”
Air tank	Model 6355RT, 3.3 gal (per retailer listing)
Tire inflation	Up to 39” tires (734 series)
Install	Bolt-on; no drilling, cutting, or welding; spare tire retained
Known incompatibility	Mopar Power Steps (Amp Research PowerStep is compatible)
Warranty	Extended 2-year on compressor and horn assembly (-734 models)
Price	$1,499.95 (in stock at publication)

A few of these figures need context. The 157.8 dB rating comes from Kleinn, measured at 150 PSI, but Kleinn never says how far from the horn it was measured, and distance changes a dB reading a lot (see our guide to advertised vs real-world decibels). Kleinn’s Demon 730 page lists a 159.6 dB figure with the optional BlastMaster upgrade. The 3.3-gallon tank figure comes from a Desert Rat retail listing, not from Kleinn’s kit page. It’s above the Demon 730’s minimum, though Kleinn’s own horn page lists both 2.5-gallon and 3-gallon minimums in different places. The 6450RC is rated for tanks up to 7 gallons, which leaves room if you add a second tank later.

What it includes

Based on Kleinn’s “complete systems include” list and the retail component breakdown:

• Demon Model 730 triple train horns with VX6003 brass solenoid
• 6450RC waterproof 200 PSI compressor
• Model 6355RT 3.3-gallon air tank (per retailer listing) with automatic pressure switch
• Vehicle-specific powder-coated steel brackets and premium mounting hardware
• INF-1 Tire Inflation Kit: heavy-duty 24-ft kink-resistant hose with quick-connect couplers, glow-in-the-dark inflator gauge with clip-on chuck and pressure release, and a Kleinn canvas storage bag
• 1302 Air Coupler Relocation Kit: quick-connect coupler, 12 ft of airline, fittings
• Complete wiring (relay, wires, loom) plus horn button, fittings, airlines, and thread sealant

Pros

• Direct-fit brackets for the 2021-2024 Ram TRX. Kleinn says no drilling, cutting, welding, or fabrication is needed.
• Kleinn says the factory spare tire stays in place.
• Comes with Kleinn’s flagship Demon 730 horns, rated at 157.8 dB at 150 PSI and fed by 1/2-inch airline rather than narrow tubing.
• The 6450RC compressor is waterproof, fully submersible, and rated for a 100% duty cycle at 100 PSI. That fits a truck built for deep water and desert heat.
• It’s a working onboard air system too. It’s rated for tires up to 39 inches and comes with a 24-ft hose and an inflator gauge for airing up after the trail.
• The extended 2-year warranty covers both the compressor and the horn assembly, double Kleinn’s standard 1-year limited warranty.

Cons

• At $1,499.95 it’s a lot to spend on a horn kit for a half-ton truck.
• The kit isn’t compatible with TRXs that have Mopar Power Steps.
• No test distance is published for the 157.8 dB rating, so you can’t compare it directly against brands that state one.
• Kleinn’s kit page doesn’t list the tank size. Buyers have to find the 3.3-gallon figure on a retailer listing.
• Only 2021-2024 TRX trucks are listed, so standard Ram 1500s need a different kit.
• Labor is still real. The compressor, tank, horns, wiring, and airlines all have to be installed, even though the brackets bolt on.

Alternatives

• Kleinn RAMHD-734. The same Demon 730 + 6450RC formula with direct-fit brackets for 2014-2026 RAM 2500/3500 trucks, at $1,599.95. See our RAMHD-734 review.
• Kleinn Demon 730 standalone. The same horns without brackets or an air system (from $499.95 at Kleinn), for TRX owners who already run onboard air or want a custom layout. See our Demon 730 review.
• Kleinn TRX21-OBA. The same direct-fit TRX air system without horns, at $999.95. It’s worth considering if you mainly want tire inflation and might add horns later.

For a wider look at what fits Ram trucks, see our best train horn for Dodge Ram guide.

Install / compatibility notes

Check two things before you buy. First, confirm the truck is a 2021-2024 TRX. Second, check the running boards. Kleinn says the kit is not compatible with Mopar Power Steps but is compatible with the Amp Research PowerStep series. After that, here’s what the install involves:

• Electrical: the 6450RC draws up to 23 A. Run the supplied relay and wiring to the battery and protect it properly. See our guide to amp draw, fuses, and wire gauge.
• The horn button is wired separately from the factory horn circuit, which avoids the issues covered in our CAN bus / BCM horn guide.
• At up to 200 PSI, leak-check every fitting on the first fill. Our bench-test and first-fill guide walks through it.
• Mount the quick-connect coupler (from the 1302 relocation kit) somewhere you can reach easily, since it’s how you’ll use the onboard air. See our onboard air uses guide.
• The 100% duty cycle rating is at 100 PSI. For more on what that means for long tire fills, see compressor duty cycle explained.

In our editorial view, plan on most of a day for a careful first-time install. The brackets eliminate fabrication, not the wiring and airline routing. Also check your state’s horn rules before using a horn this loud on public roads.

Sources

• Kleinn — Direct Fit Train Horn and Onboard Air Systems for 2021-2024 RAM TRX — part number, $1,499.95 and $999.95 (OBA) pricing, in-stock status, fitment, Mopar Power Steps incompatibility, 157.8 dB system claim, 1/2” airline, 6450RC 200 PSI / 100% duty cycle, 39” tire rating, included-items list, bolt-on and spare-retained claims, extended 2-year warranty for -734 kits, 1-year standard limited warranty, BlastMaster upgrade options
• Kleinn — Model 730 “Demon” Triple Train Horns — 157.8 dB at 150 PSI (159.6 dB with BlastMaster), stainless steel and zinc alloy construction, 22.5” × 18.5” × 7.25” rack, VX6003 solenoid, 200 PSI max, tank minimums, $499.95 standalone price (black)
• Kleinn — Model 6450RC Waterproof 200 PSI Compressor — 200 PSI max, 100% duty cycle at 100 PSI, 2.1 CFM at 0 PSI, 23 A max draw, 11.25” × 4” × 6.5” dimensions, 7-gallon max tank, 2-year warranty
• Kleinn — Direct Fit Train Horn and Onboard Air Systems for 2014-2026 RAM HD 2500/3500 — RAMHD-734 $1,599.95 price, 2014-2026 RAM 2500/3500 fitment, Model 230 kit option on the RAM HD page
• Desert Rat — Kleinn TRX21-734 Onboard Air System w/Horns — $1,499.95 price cross-check, Model 6355RT 3.3-gallon tank, 150/200 PSI compressor rating, XCR 2.0 coated spun steel trumpets

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