An oil temperature that reads a few degrees high, a fuel pressure that wanders when the alternator comes on, a radio that won't talk to the display: on a new panel, each of these can come back to a ground. A builder wiring a panel runs nearly as many ground wires as power wires, and where those grounds meet decides whether the instruments agree with each other.
Dynon's SkyView HDX installation guide (Revision AX, July 2026) puts the rule in one sentence on page 4-12: "Ensure that all external devices that interface with SkyView have a common ground with SkyView. If a device does not share ground with SkyView, it may not communicate properly." Each display's harness has two solid black primary ground wires, beside the two red power wires.
Why the engine monitor cares most
The guide is more pointed in its engine monitor section ("Engine Sensor Accuracy and Grounding," page 7-47). It calls it "vitally important that all engine sensors, your SkyView display, your SV-EMS-220/221 modules, and electrical system all share the same ground, and that there is virtually no measurable voltage between these grounds."
The reason it gives is the alternator. Large currents flow between the alternator and the rest of the airplane, and their ground is shared with the sensors. In Dynon's words, "resistance in grounds that cannot be seen with a simple multimeter can still lead to significant voltage offsets," and those offsets show up as errors in sensor readings. The same large currents run between the battery ground cable and the airframe, and along the grounding points for the avionics bus. The guide asks that all of those paths "be appropriately sized for the loads involved," with connections that are "clean, solid, and devoid of contamination."
Its test is a voltage, not a resistance. A meter set to ohms may show next to nothing across a joint that still drops a measurable voltage once alternator current flows through it.
Dynon asks for a ground wire from the engine block, or from the avionics ground block, to one of the engine monitor's ground pins. It also warns against expecting that wire to fix a poor main ground: a small wire run beside a much larger one picks up the load, is itself resistive because it is small, and makes no real difference. The fix is the big path. The guide adds that the same insufficient grounding that throws off engine readings "can lead to weak starting, hot wires, and corrosion."
The ground block
The common way to give every ground one place to meet is a single brass block of tabs on the firewall, with one heavy bolt. Each instrument's ground wire ends in a quarter-inch Faston (push-on) terminal and plugs onto its own tab, so the wires are not stacked under one nut and any one of them can be pulled off for troubleshooting.
Stein Air's product pages describe two such blocks:
- 24 Tab Grounding Buss (BB-24TAB), $85. A brass plate 3.5 inches long and 1-3/8 inches wide, with a 5/16-inch bolt 1-1/8 inches long, three washers, a star washer and two nuts. Stein says it "attaches to the firewall and is used as a common, single grounding point for all your avionics and electronic devices." It takes 1/4-inch Faston terminals and 5/16-inch ring terminals.
- 48 Tab Grounding Buss (BB-48TAB), $95. The same use, with a 1-3/8-inch bolt and twice the tabs.
A builder who would rather make one sells a 10-tab strip of heavy-gauge brass with quarter-inch Faston tabs (SA-9900, $2.25) "for making ground blocks."
Dynon's tool list for its engine sensors names a Faston and ring terminal crimp tool, B&C Specialty Products' RCT-1, among others. A loose crimp is a resistance of its own; Hangar Debrief's piece on crimped terminals covers the tool and the joint.
Planning it
Counting grounds before ordering a block saves buying a second one: two for each SkyView display, the engine monitor's, and the grounds named in the manual of each radio, transponder, autopilot servo, audio panel, light and pump the airplane carries, plus spares. The heavy wires are a separate matter. The guide gives no wire gauge for the battery and engine grounds; their size comes from the current they carry, and Hangar Flying's wire size calculator (hangarflying.com/wire-size) works out the smallest wire for a given current and length of run.
The manual for each box remains the authority for that box. Where an instrument maker's installation guide asks for a ground at a particular point, or a shield grounded at one end only, that instruction comes before any general practice.
Sources
- Dynon Avionics, SkyView System Installation Guide, Revision AX (July 2026; listed on Dynon's SkyView documentation page dated Aug. 6, 2026): "Power Input" and "Grounding," page 4-12; "Engine Sensor Accuracy and Grounding" and "Tools and Equipment Required," pages 7-47 and 7-48. Read Nov. 11, 2026.
- Stein Air, 24 Tab Grounding Buss, 48 Tab Grounding Buss and Ground Strip, 10 Tab. Prices as listed Nov. 11, 2026.
- Photo: Garmin, AERO 2018, Friedrichshafen (1X7A4801).jpg), Matti Blume, April 18, 2018. CC BY-SA 4.0. Reduced to 2,400 pixels wide.