I wish I had a good link on "vehicle electrical bonding [or continuity]"; essentially, one wants the electrical flow back to the electrical generating source (alternator) to be as good, as nearly efficent, as the one carrying electricity to the component. Although I haven't yet searched that realm, I would imagine that marine-oriented Web boards would be helpful (full-time cruising; live-aboards; passage-makers/trawlers, etc).
12-negative ground vehicles use the body and/or frame as a common ground. That is, the wiring carries the juice outwards, and the body/frame carries it back [the ground wire should really be the same gauge as the positive wire].
Headlights, HVAC systems, power seats, heated seats and windshields, "big" stereos, are all heavy amperage users and benefit by dedicated grounds (as do aftermarket ignition systems, HAM radio transceivers, etc). One may also consider the use of relays to operate the component if not already so equipped (headlights, usually).
There tends to be resistance at every point in the system -- be it a termination, a splice, etc -- and time and corrosion increase this resistance.
OEMS use wiring that meets a certain minimum; and the lack of a negative harness (in conjunction with the "positive" harness) makes for easy trouble-shooting, cost & weight reductions, etc.
But not for long-term, trouble-free perfomance (10 or more years here in Texas; shorter, perhaps in some rust-prone areas).
Todays cars are, obviously, highly sensitive to minor fluctuations a 1965 Chrysler, Ford, what-have-you would have never noticed in its operation.
My favorite story of the "horrors" of computer-controlled cars was one about the owner of a (newly-downsized) 1985 Cadillac Seville. The car would cut out and die, and the dealer and manufacturer reps were having a helluva time replicating it. In the end (dozens of attempts over 6-months or more) someone found that -- between two of the brains -- a wire carrying a signal would "overheat" (too much resistance) in crossing over the trans hump/firewall junction. The problem was an electrical drop of
one-half of one millivolt .
I could not imagine ever wanting to try to trace out anything remotely close to that.
When I wrote that most cars are deficient in this regard, one need only take a look at any item which is isolated from the common ground (radiators on many cars); or the undersized cabling going from firewall to engine block; the battery negative only grounding the body, but not itself to the engine block; etc.
The addition of some 4-ga cables can go a long ways for the above [underhood]; and a dedicated set of grounds for high-amp use components isn't too hard to figure out. No paint under connections, use of star washers on sheetmetal (with a dab of Loctite); covered with an electrical supply house conductive grease -- used sparingly -- that will prevent corrosion (not dielectric grease). Cleaning connections, keeping air and moisture out, ought to be part of ones annual checklist/to-do list.
Ideally, there would be but ONE ground on the engine to connect these to; best nearest the alternator. And, if possible, not ever going without a constant 12V source when possible (such as when switching batteries).
Same goes for adding accesories: do it properly, with a high-quality, aftermarket junction box instead of adding wires to the battery.
A little overkill can go a long way, IMO. Sort of like extending transmission and axle vents to a point above where water can get into those assemblies in flooded conditions. Peace of mind.
Sort of like a UOA for trending use and preventing small problems from becoming large ones in the quest titled, "Driving It Forever".
[ November 17, 2003, 01:30 AM: Message edited by: TheTanSedan ]
