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1.6 Ignition Signal Distribution

Blue Sea MaxiBus 2105

Type: Common BusBar

Model: Blue Sea 2105 MaxiBus

Manufacturer: Blue Sea Systems

Product Page: MaxiBus 250A BusBar

Overview

Distributes low-current 12V ignition sense signal to non-critical convenience devices. With the keyswitch removed (see Keyless Ignition), the bus bar input is now sourced from the ECM Ignition Relay — a switched relay driven by PMU OUT24 whenever the state machine is in RUN or CRANK.

Location: Cabin side of firewall

Function: Signal distribution only (not a power bus)

Critical Systems Use Dedicated Wires

Critical engine and power management systems take their own switched supply directly from the ECM Ignition Relay (or PMU OUT24 tap), NOT through this bus bar, for maximum reliability. This includes:

- **PMU 12V Switched Input (Physical Pin 7):** Direct wire from ECM Ignition Relay output - see [PMU Inputs][pmu-inputs]
- **Starter Control:** Hardware crank chain (push button → brake → P/N relay → engine-running lockout → Cole Hersee) supplied by PMU OUT24 - see [Starter System][starter-system] and [Keyless Ignition][keyless-ignition]

**Note:** PMU "Pin 7" (physical connector pin for 12V switched power) is different from PMU "In 7" (digital input channel #7 used for CT4 headlight status).

Specifications

  • Rating: 250A AC/DC continuous, 300V AC / 48V DC max
  • Terminals: 12x #10-24 screws, 2x 5/16"-18 studs
  • Dimensions: 7.93" L x 1.50" W
  • Accessories: Insulating cover (Part 2718)
  • Full Specs: Blue Sea 2105

Stud/Terminal Assignment

Stud/Terminal Connection Wire Gauge Distance Max Current Notes
Stud 1 (5/16") ECM Ignition Relay output (INPUT) 18 AWG ✓ Through firewall (engine bay → cabin) ~80mA total 5A inline fuse at relay
Stud 2 (5/16") [Available] - - - Future high-current signal
Terminal 1 (#10-24) Command Touch CT4 18 AWG ✓ ~3 ft ~20mA Ignition sense for turn signal auto-cancel
Terminal 2 (#10-24) SwitchPros SP-1200 18 AWG ✓ ~4 ft ~20mA Pin 3 (Lt Blue) - ignition sense
Terminal 3 (#10-24) Fusion MS-RA670 Radio 18 AWG ✓ ~2 ft ~20mA Yellow wire - ignition sense
Terminal 4 (#10-24) BCDC Alpha 50 18 AWG ✓ ~12 ft ~20mA Blue wire - activates charging when engine running
Terminal 5 (#10-24) [Available] - - - Future ignition-switched device
Terminals 6-12 (#10-24) [Available] - - - Future expansion (7 terminals)

Utilization: 5 of 14 used (1 stud + 4 terminals used, 1 stud + 8 terminals available)

Mounting

Location: Cabin side of firewall, behind dash (former keyswitch location now repurposed)

Benefits: Single firewall penetration (input only — from ECM Ignition Relay in engine bay), all outputs routed within cabin