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1.7.2 Firewall Ingress

All firewall penetration points for wire routing between engine bay and cabin.

Cummins Bulkhead Connector

Size: 2" diameter hole with factory bulkhead connector (self-sealing)

Contents: Factory Cummins interior harness - ECM signals, accelerator pedal, warning lamps, J1939 CAN tap to Dakota Digital

Deutsch HDP20 Bulkhead Connector

Single weatherproof bulkhead connector for all custom wiring through firewall.

Connector Specification

Component Part Number Description
Receptacle HDP24-24-21PE-L015 21-pin bulkhead receptacle, flange mount (engine side)
Plug HDP26-24-21SE 21-pin plug (cabin side)

Insert Arrangement 24-21: 4× size 12 + 17× size 16 contacts

  • Size 12 contacts: 12-14 AWG, 25A (4 available, 0 used - reserved for future)
  • Size 16 contacts: 14-20 AWG, 13A (17 available, 17 used)

Mounting: Single 1.5" diameter hole in firewall

Sealing: IP67/IP68, bayonet quick-connect coupling

Why Single Connector

RF interference analysis determined that with ferrite chokes on radio power leads at the radio end, all circuits can share one connector safely. The temp probe routes separately to grille (not through main connector).

Pin Assignment

Engine Bay → Cabin (7 wires)

Pin Circuit Gauge Source Destination Contact
1 GMRS Radio power (+) 14 AWG PMU OUT6 Midland G1 #16
2 Ham Radio power (+) 14 AWG PMU OUT12 iCom IC-2730A #16
3 STX Intercom power 14 AWG PMU OUT20 STX intercom #16
4 Brake lights 16 AWG PMU OUT21 Rear tail lights #16
5 Reverse lights 16 AWG PMU OUT22 Rear tail lights #16
6 DRL/Parking 16 AWG PMU OUT23 Rear tail lights #16
12 Ignition signal bus feed + dash button supply 18 AWG ECM Ignition Relay output (EB) Ignition signal bus bar (cabin); also taps to dash push-button supply #16

Cabin → Engine Bay (10 wires)

Pin 12 was reassigned from "Ignition sense" (cabin→EB) to "Ignition signal bus feed" (EB→cabin) when the keyswitch was removed.

Pin Circuit Gauge Source Destination Contact
7 Right turn signal 14 AWG CT4 SW1 Right fender + rear #16
8 Left turn signal 14 AWG CT4 SW2 Left fender + rear #16
9 Low beam headlights 14 AWG CT4 SW3 LP6 Pin 1 (both) #16
10 High beam headlights 14 AWG CT4 SW4 LP6 Pin 4 (both) #16
11 Horn button trigger 18 AWG Steering wheel button PMU In 1 #16
13 Brake switch 18 AWG Brake pedal switch PMU In 2 #16
14 A/C request 18 AWG HVAC controls PMU In 9 #16
15 Push button → PMU + crank chain 18 AWG Dash push-button (NO) PMU In 5 + brake switch start tap #16
16 Winch control IN 18 AWG Dash rocker switch Winch contactor #16
17 Winch control OUT 18 AWG Dash rocker switch Winch contactor #16

Reserved (4 pins)

Pin Contact Notes
A-D #12 Size 12 cavities — candidate slots for outstanding keyless system signals (fob present, gated start return); will need size 16→12 reducer crimps or size 12 contacts on 18 AWG wires

Keyless Ignition Outstanding Pins: Two additional pins still need allocation:

  1. Boomerang fob present (cabin → EB): Bullet 230 output to PMU In 4
  2. Gated start return (cabin → EB): brake switch start tap → engine bay P/N relay

Current 17 size-16 contacts are fully assigned. Options under consideration in Keyless Ignition: use two of the size-12 reserved cavities, or add a small secondary connector for keyless signals.

Separate Routing (Not Through Main Connector)

Cabin → Grille (Small Grommet)

Circuit Gauge Source Destination Notes
Outside temp probe (+) 22 AWG BIM-17-2 SEN-15-1 (grille) Twisted pair
Outside temp probe (-) 22 AWG BIM-17-2 SEN-15-1 (grille) Twisted pair

Routing: Separate small grommet near grille area - keeps analog sensor isolated from power circuits.

Radio Grounds (Floor/Frame Routing)

Radio grounds do NOT go through firewall - they route through cab floor to START battery:

Circuit Gauge Source Destination
GMRS Radio ground (-) 14 AWG Midland G1 START battery negative
Ham Radio ground (-) 14 AWG iCom IC-2730A START battery negative
STX Intercom ground (-) 14 AWG STX START battery negative

Routing: Radios (cabin) → under seat/floor → frame rail → START battery negative (driver wheel well)

Wire Count Summary

Gauge Count Circuits
14 AWG 7 Radio power (3), CT4 outputs (4)
16 AWG 3 PMU lighting outputs
18 AWG 7 Switch signals (5), winch control (2)
Main Connector 17 HDP24-24-21
22 AWG 2 Temp probe (separate grommet)

Connector Bill of Materials

Part Number Description Qty ~Price
HDP24-24-21PE-L015 21-pin receptacle, flange mount 1 $35
HDP26-24-21SE 21-pin plug 1 $25
0460-202-16141 Size 16 pin, solid, nickel 17 $0.50 ea
0462-201-16141 Size 16 socket, solid, nickel 17 $0.55 ea
114017 Sealing plug, size 12 cavity 4 $0.25 ea
114018 Sealing plug, size 16 cavity 4 $0.25 ea

Estimated Total: ~$80

Crimping Tool: HDT-48-00 (size 12-20 solid contacts)

DRL Auto-Off Signal

Note: The DRL cutoff signal does NOT require a separate wire through the firewall. The CT4 SW3 (low beam) wire is tapped on the engine bay side after it passes through the connector:

CT4 SW3 (cabin) → Pin 9 → [ENGINE BAY TAP to PMU In 7] → LP6 headlights

PMU In 7 receives the headlight status signal from this tap, enabling DRL auto-off logic.