Application Note: Electrical Grounding Concerns
The electrical environment inside a car provides unique challenges, combining high voltages and currents, low-voltage signals, convoluted signal paths, and variable conditions (i.e., fans turning on and off, or starter cranking).
When using precision electronics, it is important for ALL electronics to share a common ground. Remember that “Ground” is more than just the return path for any circuit- it is also the reference against which any voltage is measured.
Since it is not always practical to ground every device to the exact same location, here are some tips on grounding:
- The BEST grounding scheme is all grounds (i.e., ECU, Gauges, LC1 heater, LC1 system, etc.) SOLDERED into a single lug and bolted to the engine block.
- The next best is all grounds attached to the same source, as close as possible, but on separate lugs. This is because even the corrosion between lugs can create ground offset and noise. Incidentally, this is why many ECUs have separate ground wires for injectors vs. ECU system ground- separating high voltages and low voltages reduces noise.
- Grounding to the engine block is usually better than grounding to the frame.
- Grounding a gauge to the radio is usually bad- ground offset can vary with volume.
- Grounding to an ECU housing is generally not optimal- housings are strapped to the frame for shielding, but not necessarily grounded.
- One of the WORST things to do is to ground most of your electronics to one place (i.e. the engine block), but ground one device somewhere else (i.e., the frame). Not only can this result in ground offsets, it can also create a “path of least resistance” for high currents THROUGH a low-current device. This can result in melted wires and vaporized diodes, when, for example, starter currents flow through gauges.