VEHICLE GROUND
by bd
THE SIGNIFICANCE OF GROUNDAn electric power source enables various wiring, connections, electrical controls, and components, collectively referred to as a circuit, to achieve a purpose. Without power, a circuit is merely a vacant
"potential" pathway that promises appliance operation without actually delivering it. Consequently, a power source is fundamental to circuit operation, and good connections are crucial. This is obvious. There is no revelation in this — until we look closer. Electric circuits consume energy. Theoretically, every electrical component, whether an appliance, switch, or interconnecting wire, consumes voltage in proportion to the resistance the component presents to the current flowing through it. This occurs because every known conductor possesses an inherent resistance to current flow, however slight. As voltage and current power an electric appliance,
100% of the voltage applied across the appliance is consumed in forcing current flow through the resistance thereby represented. The current is neither depleted nor altered by the appliance but is limited in intensity by the resistance encountered and the voltage applied. This law applies to every component in the circuit, such that
100% of the voltage applied across the circuit is divided proportionally between each component comprising the circuit, according to its resistance. In practice, for wires properly matched in gauge to the current they must conduct, the maximum allowable voltage consumed by the wiring is limited by design to a nominal amount (typically <3% total, or <0.4 volt maximum in a 14-volt circuit). Generally, operating voltage losses are much lower because continuous-duty circuits are rarely operated at maximum capacity. Thus, the voltage loss (aka, drop) across the wiring of a properly constructed circuit, under normal circumstances, can be considered negligible (<<3%).
In application, a power source and its connected components create an uninterrupted current pathway that loops
from the power source
through a designated appliance
back to the power source. "Ground" is that specific section of the circuit that
returns current to the power source
directly from the last designated appliance in the circuit without experiencing an appreciable voltage loss, typically <<1.5%. Why <<1.5% instead of <<3%? Often taken for granted, 'ground' is roughly
one-half of every electrical circuit. It is one-half of the framework around which everything electrical is constructed, tying the various pieces together to achieve a functioning system. One-half of 3% is 1.5%. Therefore, the voltage loss across just the ground path can be crudely approximated as <<1.5% of 14 volts, or <<0.2 volt,
assuming the ground path is an electrical wire or cable. BUT (…there is always a caveat…), if the ground path is the steel body or frame of the vehicle and all connections to the body, frame, and battery are clean, tight, and fully serviceable, then voltage loss across that ground path will be so low as to be virtually unmeasurable. Can you suggest a reason why?
Hint: It involves the effective relative cross-sections of the conductors. The effective cross-sections of the body and frame are huge compared to the cross-section of a wire or cable. Even though steel has ~7–12 times (depending on the alloy and temperature) greater electrical resistivity than copper, there is so much steel that its greater resistivity is inconsequential.
In a real sense, 'ground' is the baseline within any given electrical system on which every electrical component relies to function correctly.
For electrical systems in general, as the power source return path, 'ground' is defined as the system-wide reference of zero potential, zero voltage, zero electrical energy. All meaningful comparisons of electrical energy and work within a circuit depend on ground. Essentially, it is the controlled, hence, the predictable divergence of voltage away from zero (ground) that makes electricity useful. Circuit voltages are specified and measured relative to ground; hence, voltage is either positive, zero, or negative relative to ground (that is, above, equal to, or below
zero electrical potential). To ensure proper circuit function, ground connections and throughput must be perfect! There is no room for error, especially when circuit complexity increases with multiple circuits sharing a common ground path. Any error occurring in the ground baseline broadly compromises the electrical functions of all circuits sharing that ground — more on this in the subsequent section.
Automotive electrical systems possess a single ground reference. Within specific contexts, ground is also referred to as chassis, common, and earth. On a broad scale, ground is considered fully comparable to the electric potential of the body and mass of planet Earth, defined as unvarying and zero. Traditionally, ground is the power source (e.g., battery, generator, alternator) zero-voltage electrical terminal comprising the metallic frame and body (chassis) that supports, surrounds, and shields the various components and circuitry of the vehicle's greater electrical system. Because the vehicle's steel chassis embodies ground, connections to ground are conveniently available wherever needed, saving on the expense and complexity of routing additional wire.
Virtually all vehicles manufactured since the mid–1960’s use negative polarity ground systems. As a result, measured voltages are generally zero or positive relative to ground. Bear in mind, however, that from manufacturer-to-manufacturer there are no assurances that the system ground is, in fact, the negative side of the power source. Therefore, when in question, it is prudent to verify ground polarity through direct observation and measurement.
To help alleviate the development of ground errors in aging microprocessor-equipped vehicles, beginning in the early 1990's, General Motors' medium and heavy truck divisions abandoned using the metallic chassis and bodies of their vehicles as the universal ground path in favor of dedicated ground cabling that connected directly to the negative terminal of the battery. Thereafter, GM considered appliances to be properly grounded
only if and when they were effectively connected directly into the network of ground cabling.
HIDDEN INFLUENCES OF "FLOATING" GROUNDSConsistently flawless and uniform ground connections are crucial to the proper function of
every electrical system; imperfect grounds are a nemesis. Occasionally, electrical systems suffer from unwanted multiple ground levels that are not uniformly zero. For example, the ground bus for a sub-circuit or network of sub-circuits can serve as a "proxy" or "false" ground if it is
above or
below, rather than equal to, the primary system ground due to electrical isolation from the ground reference terminal of the power source (which is true zero). Such isolation results when a poor intermediate connection exists in the ground bus
somewhere between the sub-circuit(s) and the ground terminal of the power source. Non-zero ground levels are said to "float" above or below ground.
'Floating grounds' are universally undesirable! Electrically energized components connected to a 'floating ground bus' may seek alternate return paths to B- through the non-energized components that are paired with (share) the 'proxy' ground. In other words, circuits back-feed. The resulting symptoms are senseless, unpredictable, and often quite wild!
Floating grounds can occur from errors in (re)assembly or develop over time from loose, broken, burned, or oxidized connections within the ground path. They typically produce bizarre symptoms that, at first encounter, can be difficult to rationalize and diagnose. Under the right circumstances, floating grounds test the patience of even the most seasoned electricians. Weird, inexplicable combinations of lights, wacky gauge indications when electrical appliances are switched ON, completely inoperative electrical equipment, and electrical appliances that
randomly operate when switched OFF are telltale signs of floating ground problems. One light dims while another brightens; relays randomly buzz and click; the dash lights illuminate when the wipers are switched ON, yet the wipers don't work; turn signals illuminate dimly but don't flash; dash lights dim when a door opens — the irrational combinations of symptoms are endless. In cases where the engine ground connection to B- is poor, unpredictable ground current paths may establish through drivetrain components such as transmission, u-joint, and drive axle bearings, or transmission cooler steel lines — even through liquid engine coolant — resulting in electrolysis and destructive erosion of bearing surfaces and metal castings. The aluminum components used in many engine cooling systems are particularly susceptible to floating-ground-induced electrolysis.
Resolutions to floating ground problems become easier with experience and familiarity with factory ground locations. Patience is key. Ultimately, the solution to floating ground issues is routine and methodical:
study the relevant wiring diagrams as needed, based on which appliances are affected, to systematically locate and repair the offending ground connections, supplementing with additional ground connections if necessary.SERVICING THE GROUND PATHNever take an electrical system ground connection or pathway for granted! The importance of good ground connections cannot be overstated! Impaired ground paths cause a myriad of bizarre symptoms when quasi-energized circuits haphazardly function due to unpredicted, substitute ground paths. Faulty grounds can be responsible for mysterious engine shut-downs and random “Check Engine” light activity on electronically controlled engines or random illumination of the instrument cluster turn and high beam indicators when the horn button is pressed. Perhaps the wipers stop working on the high fan setting of the heater blower. Such bizarre and intermittent symptoms always suggest a poor ground — not as an assurance, but statistically!
General service considerations:Star washers promote corrosion between a grounding surface and its connected terminals by decreasing the surface area of contact while allowing the ingress of moisture, dust, and corrosive salt. Hence, star washers should be avoided at any connection carrying three amperes of current or more. Specific connections to exclude star washers are blower motor ground, alternator ground, engine block ground, engine-to-cab ground, frame rail grounds, radiator support grounds and starter motor connections. Star washers in such circuits should be removed and discarded, and then the connecting surfaces cleaned, burnished, and coated with an antioxidant as specific problems are addressed.
Except at the starter motor, a hardened steel flat washer may be used between the heads of bolts and ring terminals. The outside diameter (OD) of the flat washer should be the same OD or slightly larger than the OD of the terminal(s). Split lock washers may be used between the bolt heads and the flat washers. On starter motors, ideally, a shoulder-nut (aka, flange nut) should bear directly against the terminal ends slipped over the large battery cable stud of the solenoid.
For general-purpose soldering of electrical splices and/or terminals, use 0.028" - 0.040" diameter 60/40 (Sn/Pb), 63/37 (Sn/Pb), or 70/30 (Sn/Pb) rosin core solders, ONLY. To repair/resolder rigid printed circuit board foils and through-hole component solder joints that have sheared from standing wave vibrations, substitute 1% - 7% silver-bearing (Sn/Pb/Ag or Sn/Ag) rosin core solder to take advantage of its increased shear strength.
To effectively insulate and seal bare electrical splices and wire-to-terminal connections, use dual-wall, adhesive-lined, polyolefin heat shrink tubing (aka, marine grade heat shrink). Be sure to slip the tubing, precut to the proper length, over the wire before attaching the terminal. Shrink the tubing evenly using a heat gun (the safest method), a micro torch adjusted to a low temperature reducing/carburizing (yellow) flame, a match, a lighter, or similar heat source.
WORK SAFELY! If using an open flame, be very careful of flammable vapors and materials that are in proximity to your workspace! Move the flame continuously to prevent scorching of the tubing or wire insulation. Allow at least three minutes of cooling time before handling.Replace Scotch-Loks
® with properly crimped, soldered, and shrink-sealed splices or substitute suitable modular terminals that are housed in molded connectors. The ID of ring terminals should closely match the OD of attachment hardware, just as mating slip-fit terminals should be correctly matched in size. Replace all broken, deformed, or improperly sized ring terminals using bare, plated (tinned), heavy-duty copper or brass terminals. Strip, clean as necessary, mechanically crimp, and then solder stranded wire to the bare terminals. Once cool to the touch, insulate the terminal shanks, overlapping the wire insulation, using marine-grade heat shrink. Inspect ring terminals for mispositioned insulation or adhesive residue that partially shrouds or covers the clamping surfaces of the ring and trim accordingly.
Always place the ring terminal carrying the greatest current closest to the ground source (which generally should be located at the base of the junction). Or, if all circuits support roughly equivalent current loads, place the ring terminal with the largest outside diameter (greatest surface area) closest to the ground source (base of the junction). Grounding surfaces should be clean, shiny, bare metal. Ground connections between dissimilar metals or those exposed to weather or corrosive environments should be liberally coated with a high-quality antioxidant paste, such as Truck-Lite NYK-77 compound, Gardner Bender Ox-Gard, or thick white lithium grease to help reject moisture and salt and retard electrolysis and corrosion.
Should a ground bus simply become overburdened by current flow, the only solution is to augment the ground path with additional or upgraded cabling and connections. In some cases, this means increasing cable size. In other cases, it may mean reorganizing the sequence of ring terminals within the stack and/or increasing the number of ground attachment points. Still, other cases may require reforming or replacing terminals to correct terminal distortion or improper sizing. For example, the
maximum combined voltage drop allowable across an alternator charge lead and the ground bus is 0.5 volt when the current output from the alternator is at maximum. If an upgraded alternator with increased current output capacity is installed on a vehicle, both the alternator charge lead
and the alternator ground lead, if used, may require replacement with larger gauge cabling to handle the additional current flow. Otherwise, the alternator’s output voltage may be consumed by the cabling, and the batteries will charge no better than before the alternator was upgraded.
Another example: the individual connections and wiring within a ground system may be "independently" perfect. Yet, when the individual ground wires are assembled into a column of ring terminals stacked under a bolt or screw, current flow can become opposed by cumulative resistance if the effective cross-sectional area anywhere within the column of terminals or between the column and the point of connection to the ground bus (chassis) becomes inadequate. The result is a 'floating ground' with a portion of the system voltage consumed and wasted across the shared attachment point and/or any alternate ground path that occurs. One possible solution is to reorganize and distribute the individual wires amongst multiple ground attachment points while ensuring that the rings are properly sized, flat, and undistorted to eliminate unwanted gaps between rings. Remove any star washers encountered.
Another example: a 10-amp air control solenoid for bags shares its ground attachment point to the cabin sheet metal with the instrument lamps. Now, every time the bags are charged or emptied, the instrument lamps glow dimly. The cause? A poor connection creating a 'floating ground' that backfeeds the instrument lamps. Why? The ground attachment is overtaxed by improper stacking of the ground terminals; although both rings are sized for a #8 screw, the large OD heavy-duty ring for the solenoid is stacked on top of the small OD ring for the instrument lamps; a factory star washer sits between the small ring terminal and the cabin sheet metal. A workable solution is to reorganize the order of ring stacking and burnish the cabin sheet metal attachment point to shiny bare metal, such that it matches the larger OD of the heavy-duty ring. Reassemble without the star washer and add a liberal coat of antioxidant paste.
Essentially, as the current load on a system or sub-system is increased effectively beyond its original design capacity, such as by upgrading or adding appliances that increase current flow, or from stacking too many ground wires onto a single attachment point, or by feeding too many subordinate grounds into an overtaxed common bus, the system must be adjusted and upgraded adequately to compensate for the increased demand.
Specific service considerations:Thoroughly burnish and clean the battery cable connections! Employ a specially configured battery terminal brush (image) to service conventional post-style connections. Avoid applying acid neutralizers directly to or around the battery. Acid neutralizers consist of chemically active bases that react with the acid to leave conductive salt residues nearly as damaging as the acidic battery electrolyte. Instead, substitute clear water and a nylon bristle brush to wash away accumulated dirt and corrosive films. Be sure that battery caps are fully installed before and while cleaning the battery! Thoroughly rinse all surrounding painted surfaces until totally clean of chemical splash from the cleaning process. Check for proper torque of cable attachments and remove any paint or corrosive salt encrustations. Check for uneven solder accumulation on all of the battery cable terminal ends. Scrape, sand, or buff away excess solder accumulation to ensure clean, uniform, flat, or otherwise conforming clamping surfaces.
Inspect for star washers, loose connections, and corrosion wherever battery cables are fastened to a battery disconnect switch, relay, junction block, or the starter. Check for large diameter star washers at the engine block ground stud or bolt. Discard any star washer(s) encountered, then thoroughly clean, burnish, assemble, and coat the connections with a good antioxidant paste.
Check the tightness and integrity of all connections to the cab ground points on both sides of the firewall. Remove any star washers discovered and service the connections as required, coating them with a high-quality antioxidant paste.
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