You're probably here because you found an issue in your electrical system! This article gets right to the point with some easy tips and tricks, dos and don'ts. If you're struggling with erratic readings, flickering screens and back-feeding signals, you're in the right place! We've been doing this for decades and we've seen it all!

Let’s start with grounding.  Grounding is the other half of the vehicle electrical system that we often overlook.  Just drilling a screw into the sheet metal isn't always going to be the answer.  Let’s start with some basics.

What can a bad ground or ground loop do to your gauges and other sensitive electronics? Other than making them mis-behave, internal component damage/failure can occur.  This happens when the ground for the component is poor and when the item is powered up, the additional current required flows through another point in the system.

Why is this bad?  When over-voltages are in the system at the component level, excessive current/amps are drawn through parts that are not designed for that amount of power.  For example, we see this on our programming buttons from time to time.  They use ground input to trigger the selections.  If the gauges aren't grounded correctly, the current will flow though that button circuit and damage the components on that part of the board making the button stuck in the "ON" position. "Stuck in setup".

Ground connections must be clean using good quality wire of the correct gauge.  They should be metal-to metal, you may need to grind or sand off paint to get a good connection.  We often forget that an older vehicle that’s being built up with more electronics was never meant for that load, so the wiring and grounds need to be updated.

Battery/engine grounds: This is the #1 culprit in vehicle grounding/noise/EMI.  That old ground strap may look OK but it’s probably deteriorated over time with corrosion around the terminals.  It’s a cheap, easy update/upgrade.

Below is an image of a deteriorating ground strap.  The patina here is a bad thing.  You may get away with cleaning things up by removing the connection and sanding for a while, but once it’s this corroded, it is probably best to just replace it.

Let's start with the basics.  The image below depicts a simplified vehicle wiring diagram.  The goal is to have the least connections possible.  The more connections, the higher the risk of a poor connection or ground loop.  

The big thing to notice here is how the vehicle is grounded.  The chassis and block share a connection for the battery negative terminal.  This avoids a ground loop and will dramatically reduce any noise in the system.  It also ensures that the voltage drop is the same on the block and the chassis.   All items should be grounded to the chassis.

Testing a Ground

Use a digital multimeter set to measure resistance (Ohms, ) or voltage drop (DC Volts).

1. Resistance Test (Ohm Check):

2. Disconnect the battery (for safety).

3. Measure the resistance between the battery's negative terminal and the grounding point of a component (e.g., a headlight bucket).

4. A good ground should read very low, typically less than 1 Ohm (and ideally close to 0). A higher reading indicates excessive resistance.

If you're using our SNAP-ADAPT connector, make sure to test the ground at the pin once its plugged in.  The factory plugs have been exposed since who knows when.  Dirty and bent pins that do not have a good connection are a major contributor in grounding issues.

Voltage Drop Test (Under Load):

1. Set the multimeter to DC Volts and turn the circuit ON (place it under load, like turning on the headlights).

2. Place the negative probe on the battery's negative terminal and the positive probe on the grounding point of the component you are testing.

3. The reading should be very low, ideally less than 0.1 Volt (100mV). A reading higher than this means the ground connection is losing voltage due to resistance, robbing the component of power.

Ground-Related Causes of EMI/RFI

1. Ground Loops and "Dirty" Ground Signals

The most common and notorious issue is the ground loop, which is directly tied to poor grounding practices.  In short, the ground has 2 pathways either through multiple grounds or through another component in the circuit.  This is common with engine senders used with a bad ground strap.

1. The Cause: A ground loop occurs when two electrical components are grounded to different physical points on the chassis or body that have a slightly different electrical potential (voltage).2 This difference, often due to corrosion or high resistance in the main ground path, creates a secondary, unwanted return path.

2. The Effect (The Noise): This potential difference causes a small but continuous current to flow between the two ground points, creating a circulating noise path (the "loop").3 The noise often manifests as a distinct alternator whine or engine RPM-dependent whine in the radio or audio system, as the noise from the alternator or ignition system is induced into this unstable ground path and amplified by sensitive electronics.

Another tip in adding new compoents to an older vehcile system is to just add a simple auxillary fuse block.  This will have its own dedicated power feed (constant and/or switched with a relay) that does not interact with the old system at all.  This should provide "clean" voltage to whatever componet you are adding, especially modern ECUs, controllers and gauges.

Yes it can really be that simple when it comes to troubleshooting ground and power issues.  If you need any additional help please make sure to reach out via our CONTACT US PAGE.

Additional resources related to this article

NVU FAQ- COVERS 99% OF QUESTIONS

ONLINE TROUBLESHOOTING: STEP BY STEP CHECKS YOU CAN DO RIGHT NOW

POWERTRAIN SPECIFIC INSTALL GUIDES

GROUNDING VEHCILES (SPEEDWAY MOTORS)

EMI TECH ARTICLE AND TROUBLESHOOTING

EMI ARTICLE (SPEEDWAY MOTORS)