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2.5 Horn System

PIAA 85115 Superior Bass Horn

Type: Dual Tone Horns

Model: 85115

Part Number: 85115

Manufacturer: PIAA

Product Page: PIAA Superior Bass Horn 85115

Mounting: Engine bay

Power Source: PMU Out 18 (7A capacity, CONSTANT)

Specifications

  • Current draw: 2.7A per horn × 2 = 5.4A total
  • Ground: Chassis ground (engine bay)

Control

Button: Momentary push button (normally open) on steering wheel PTT bracket

PMU Configuration:

  • Input: In 1 (horn button signal)
  • Output: Out 18 (7A capacity, powers horns directly)
  • Logic: When In 1 closes, Out 18 activates (no external relay needed)
  • Power: CONSTANT (works with ignition off for safety)

Wiring Configuration

START battery CONSTANT → PMU → Out 18 → PIAA Horns (5.4A) → Chassis Ground
                          ↑
                      Horn Button → In 1 (trigger)  [column path undefined — <a href="https://github.com/sob/shopmanual.io/issues/152" target="_blank" rel="noopener">TBD #152</a>]

Outstanding Items

🔴 Critical (2)

High (7)

📋 Medium (3)

  • Horn button → PMU In 1 wiring path through steering column (#152) — PMU In 1 (horn request) lists "steering wheel button" as its source, and the horn page puts the button on the steering-wheel PTT bracket — but no wire path, gauge, or connector is defined for how the button contact reaches PMU In 1 through/around the steering column. Street-legal item with an under-specified signal path.
  • iBooster Wiring Harness Selection (#105) — Select the Bosch iBooster (Gen 2) wiring harness: Tulay's Gen 2 universal (plug-and-play) vs EVcreate Gen 2 connector kit (DIY). Decision pending donor arrival and pigtail condition inspection. Tracked in the purchase tracker but was missing a TBD issue.
  • Axle Brake Flex Hose Length (#86) — DOT (FMVSS 106) braided-stainless extended-length flex at each axle - length blocked on axle + suspension selection (Section 10); size to full droop, do not cut until ride height fixed

🔍 Verify (5)

  • iBooster standby current spec (ignition-off test value) (#151) — The engine-systems testing checklist includes "Verify iBooster standby current within spec (ignition OFF)" but no standby-current spec value is documented anywhere (the brake-booster page does not state one). The test step cannot be completed as written.
  • WAIT-to-start lamp polarity: ECM Pin 35 active-low vs HDX input active-high (#150) — ECM Pin 35 (WAIT lamp, yellow) is active LOW (~0V when WAIT on, ~+12V off); the HDX indicator input is documented as active HIGH. If wired without resolving this, the cold-start indicator reads inverted — and the documented cold-start procedure depends entirely on watching the WAIT lamp.
  • Restomod Air HVAC integration — verify A/C request wiring to PMU In 9 + blower draw (#146) — The factory TJ HVAC is replaced by a custom Restomod Air electronic HVAC kit (ordered, owner-confirmed 2026-06-11) — this resolves the original "no A/C request source post-PCM-delete" gap. Restomod Air kits are fully electronic (servo-driven doors, no vacuum), and the control head generates the A/C request: compressor-engage output (12V) → trinary pressure switch (30/406 psi cutouts) → PMU In 9. PMU logic then drives OUT17 → compressor clutch.
  • AMOT 4261M 2.8″ intake air-path connection OD / reducer coupler to 2.125″ turbo inlet (#129) — The 4261M02 is a wafer butterfly valve that sleeves into a 2.8″ (71 mm) nominal intake duct; the AMOT datasheet (4261M_Air_Shutoff_Valve_0119rev2) publishes only nominal size (71 mm), bore (61 mm / 2.4″), and overall envelope — not the air-path spigot/wafer OD or clamp interface. The NPT thread in part number 4261M02A027-AA (actuator code 27) is the pneumatic control port, not the air path.
  • Grid Heater Current (#42) — Design value 80A - verify via element resistance measurement during installation (~0.15 ohm @ 12V).