Four Screens and a Compass

Introduction

The cab is the most finished subsystem on this truck and the one most likely to be taken for granted, because everything in it already works. That is exactly why it is worth documenting now: the decisions have been made, the reasoning behind them is still fresh, and in two years the question “why is there a Garmin on the dash when the tablet has GPS” will have no obvious answer unless it was written down.

This dive covers what is in the cab, why each thing is there, and where the arrangement is weakest.

1.1 What is fitted

Table 1 — What is fitted

Item	Role
Stock infotainment screen	Bluetooth to the phone, Android Auto for Waze, hands-free calling, audio
Phone	The Android Auto source; cellular; the backup for everything
Samsung Galaxy Tab S8 on a mount	Gaia GPS with offline maps and off-road overlays — the primary off-pavement navigation
Garmin eTrex Touch 25 on a Bullet dash mount	Compass mode — supplies the heading the truck does not have
RAM mount on the front seat bolts	Carries the ham, scanner, and GMRS radio heads; mixed with LIDO components
Heavy-duty floor mats, front and rear	The unglamorous one that matters most

Plus one thing not yet fitted: a harness to permanently defeat the auto engine stop/start, covered in volume four.

1.2 The organizing idea: four displays, four jobs, no overlap

The instinct on seeing four screens in a truck is that three of them are redundant. They are not, and the distinction is worth making precisely because it is the thing that justifies the whole arrangement.

The stock screen is for the road. Android Auto over the factory display handles the ninety-five percent of driving that happens on pavement: Waze for traffic and hazards, hands-free calling, audio, and the destination search that works because it is connected. It is the best tool available for that job and it is already paid for. It is not an off-road tool and should not be asked to be one — it depends on connectivity, its maps are road maps, and it has no concept of a two-track.

The tablet is for off pavement. Gaia GPS on a Galaxy Tab S8 is the primary navigation surface once the pavement ends: topographic and satellite base layers, public-land and motor-vehicle-use-map overlays, downloaded for the region before departure, with track recording. The large screen is the point — a route on a phone-sized display is legible in the driveway and useless on a moving vehicle.

The eTrex is for the one thing neither of the others reliably does. The truck has no compass. That gap is the entire reason a fourth device exists, and volume three deals with what the eTrex actually provides and where the common assumption about it is wrong.

The phone is the fallback and the uplink. It is the Android Auto source and the connectivity source, and — critically — it is the device that still works when the mount fails, the tablet is flat, or the truck’s electrics are the problem.

The overlap is the point, not the flaw. Four devices with four power sources and three independent GNSS receivers is redundancy, and redundancy is the correct posture for navigation in terrain where being lost has consequences. The failure mode this protects against is not exotic: a tablet gets hot and shuts down, a mount vibrates apart on washboard, a cable chafes through. Any one of those is a nuisance with this arrangement and a serious problem without it.

1.3 Where the arrangement is weak

Three honest criticisms, each of which is a candidate for the next round of work.

Everything depends on the same 12 V system. Four devices, all charging from the truck. A charging failure or a flat battery takes the whole cockpit at once. The tablet and the eTrex both have internal batteries, which mitigates but does not solve it — and the eTrex’s AA cells are the only genuinely independent power source in the cab. This is a real argument for keeping a set of lithium AAs in the drawer, and it ties directly into the Vehicle Power dive.

Screen real estate on the dash is finite and already contested. A tablet, a handheld GPS, and radio heads all want the same driver’s-eye volume. Adding a GMRS head or the cellular gateway’s status makes it worse. The arrangement works today; it will need re-planning if more is added, and the honest constraint is that the driver’s forward view and the airbag deployment zones are not negotiable — a point volume two treats at length.

Nothing is documented as-built. Which RAM components, which arm lengths, which ball sizes, where the power runs. This is the sort of thing that costs an afternoon to reconstruct and five minutes to photograph, and it is the main reason this dive should be photographed before anything else changes.

1.4 What is deliberately not here

No dedicated in-dash off-road navigation head unit. Replacing the factory infotainment on a new truck is expensive, forfeits Android Auto, and complicates the warranty for a capability a tablet already provides better.

No CB radio. The convoy-communication role belongs to GMRS or the ham gear, both of which outperform CB, and neither the equipment list nor the trips taken so far suggest a need.

No router display or control head. If the cellular gateway from the Cellular Gateway dive is bought, it is administered from a phone or the tablet over its own Wi-Fi. It does not need dash space and should not get any.