How do you determine the sequence of grounds in a car or that an attachment point is a haphazard one? I always make sure I have solid ground connections between the body/engine,body/frame, and engine/frame. I make sure these are good connections with larger wires which I believe gives me the "electrically continous" condition Crazy Steve mentioned.......don't mean to put words in Crazy Steves mouth, so correct me if thats wrong. Once I have all the major components interconnected, I don't see why any connection at any decent solid point would create a problem. I do consider myself to be an "electrically challenged" individual. I can see using a buss if you have a bunch of items needing grounding in the same area, like under the dashboard. On the otherhand, its not convenient for tail lights So I don't understand what determines " sequence" or "haphazard" when attaching a ground wire.
I'm "electrically clueless" are all the mentioned "Grounds" done with battery cable gauge wire? Would an equal number on both sides, cut the risks to a minimum? Bob
To answer your question, this is where the math comes in. You have to select your ground wire based upon your amperage load of your circuit, your nominal voltage, and the length of the wire from terminal to grounding point. Each gauge wire is designed to hold a certain amount of amps at a certain voltage at a certain length before thermally failing and catching on fire. Sent from my XP8800 using The H.A.M.B. mobile app
To my way of looking at it, all these things are not "ground" per se, but merely paths to get to ground, and to get to ground they all have to eventually get to that one last main path......the battery cable. If all the major players in the system (engine/body/frame) are interconnected with cables oversized for any needs, then it seems that individual unit connections can be made anywhere on frame/body/engine and provide a suitable return path. I don't see why any connection would not be proper other than one that exposes the connection to harm. Other than that, it seems any connecting point should be as good as any other connecting point. Agree/Disagree ?
Probably need to clarify/simplify some of the terminology as over simplifying it will cause more confusion, and often 'voltage' used in discussions can be confusing when it is used in reference of itself when used as a measurement, e.g. ' Battery voltage is twelve volts'. Ground or grounded will be used in reference to termination point of a ground source/point. Bond or bonding will be used in reference to making components have the same electrical potential so as to prevent unwanted stray(induced or otherwise) voltage/current 'leaks'. Potential, or difference of potential, will be used in reference to voltage, or difference of voltage, e.g. 'There is a difference of potential across a fully charged battery terminals of 12.6V.' For ease of discussion I will assume we are speaking of negative ground systems. For my fellow sparkys out there, automotive systems tend to be more series based circuits than parallel. If you remember your motors/controls classes, this is where the ole 'stop/start' circuit drawings kick in. Also if you worked on fire control circuits, things will look more familiar. If you can understand the wiring of 3/4 way switching, you will easily pickup on automotive wiring. Some of the more stranger things that occurs in automotive wiring is two(or more) circuits will share the same wire but usually not at the same time. This saves the manufacture wire/weight/cost, most notably with parking/signal/hazard circuits. With grounds, it's just like the positive wires. You will have your main ground cable and will be bonded somewhere on the vehicle body/chassis. This changes depending on what type of vehicle is being built. Some post-war vehicles may have the frame bonded, but it is not always used as the main ground bus. The frame itself may be intentionally electrically isolated from the vehicle as well, you will need to verify this on your vehicle. If the battery is near the engine, the main negative cable will be bolted to engine. Since the largest load(amps) is most likely to be the starter, this keeps heat/resistance down to allow those CCAs to turn the engine over. Also using an appropriately sized wire running parallel from the battery terminal to bond the radiator support is also a good idea, it can help out with lighting. Just because a part is bolted together doesn't always mean it is properly bonded, glue/grease/paint are good isolators. A main bonding jumper should be used from the engine to the body/chassis to properly ground. And again between the body and chassis, if needed/desired. A ground between the engine and firewall is also a good idea, as well as bonding any metal components that may be isolated but may be induced with voltage/current. There's a reason why Chevy put those little ground straps between the valve covers and firewall. Valve covers with spark plug wires running on or near them can become like a capacitor and charge up. Maybe not shock your friend fun, more like annoying 'mystery' interference in the radio or ignition components. Have a few components like that and they can stack up and cause a larger problem. Moving metal panels, doors, hood, decklid, etc should also have something bonding them. Do not rely on hinges to conduct. More than once has a slow window regulator motor has been blamed rather than a bad ground. Electricaly clean(no paint/grease/goos) tight connections are key. Use a nut/bolt connection whenever possible. I like to use a combination of serrated studs, stud bolts, or a properly drilled/tapped hole for use with a 10-32 green ground screw and a dab of anti-oxidant, electrically conductive grease. Studs make a great spot to attach a meter when troubleshooting. Check out data cabinet bonding/grounding/ground stud kits. Sheetmetal screws, self tapping or not, are totally unacceptable for a proper electrical connection. Factory did it because it was fast, cheap and 'good enough' back when. It shouldn't. As long as the body, doors, deck, hood, etc are all bonded to each other and the body is bonded to whatever is your main ground point from the battery, there should be no ground issues. Each panel should have zero potential to each other. There is something similar found on pretty much any car since mid 80's up. It will be what looks like a Lego block bolted to the body and will have up to six wires coming out of it. Look for 'firewall grounding block', no need for FAA approved pieces but you can get an idea of what is available. Tail light grounds should terminate at the nearest body panel. There is no reason to run a dedicated ground wire to the battery. As stated, as long as the complete metal body is bonded it will be electrically the negative terminal on the battery. All you need to do is bring power to whatever device and then ground it to the body. Only haphazard that may occur is if there are a bunch of needless ground wires running back to the battery. This may then cause ground loop issues where the components ground is no longer zero potential to the body. That's where we get noise and other operational weirdness from. Your main grounds/negative cable to the engine and then to the frame and/or body will be 'battery gauge' sized. With the rest of the car bonded/grounded to itself there should really be no reason to run any dedicated ground wires back to the negative terminal. Most components will run well completing the circuits through the steel body. Yes. If the body components/frame are all properly bonded grounded together then the body itself is the ground/negative terminal of the battery. Normally, highest load(amperage) will usually be the starter. It will need to complete the circuit so the stater cable and negative cable are sized the same to complete the power loop for the starter motor. Even with a high amp alternator, you probably won't run anything larger than a #6 wire from the Alt Batt terminal to the battery(+) terminal.
From my experiences in outfitting new trucks, is that the battery grounds to the engine with a very large cable. But all other OEM grounds are substantially smaller. Since we were installing high amp draw (350+) items, and using the vehicles frame as a ground, I added a designated ground directly from the negative battery post to the close spot on the frame with a cable equal to the positive cable. I made sure the paint was removed, usually with my 4 inch grinder and put a regular bolt and nut there .At one of the many schools I went too , they warned of using serrated washer or nuts on electrical connections. They have a tendency to collect moisture in the grooves and cause problems. I actually experienced this problem, right before I attended that school, so it hit home with me. I would then cover the connection with paint I always made sure our equipment had a good ground to the frame by bolting it to a clean frame, in many places. I would also weld the finial mount at the rear ensuring a good connection. I never had any problems with this method. I never considered this to be “ haphazardly adding grounds” . Just my experiences. Bones
Thank You Mad Mike for all the time you spent on your response......Information like that is very helpful to people like me who are "electrically challenged". For the most part I have followed the things and methods that you explained. I purchased one of those hydraulic crimpers that Harbor Freight sells for doing larger wires. I have some of that braided looking ground cable as well as some nice flexible copper stuff. I make good sized cables for all connections between body/frame/engine. I often weld studs to things to use for the grounds. On a "current" off topic build I'm doing,I made ground cables for the radiator support back to the frame where I added a welded stud on each . I think one of the main things you helped people with is the idea that just because two things are bolted together, we shouldn't feel that it means current will always transfer properly. Thanks again............
Mad Mike, thanks for the explanations above. I remember sitting in on a presentation on bonding and grounding from the provincial electrical authority, once, when I did infrared assessments on electrical distribution systems(commercial and industrial). I was invited to sit in, by the industrial client, just for my information. Knowledge is good.
Great post, but there's a few things that I think should be clarified in case somebody drops into the middle of this thread... One, you'll never get 'difference of potential' in circuits down to zero. If anybody accomplishes this, get a patent; you've discovered room-temp superconducting! LOL! Every wire, terminal, connection, all lose a small amount of voltage between points and they add up, the trick is to minimize that loss to acceptable levels. Now, in higher-voltage systems this is generally ignored. Electricians rarely calculate this as the loss as a percentage of the source voltage is usually well within the voltage tolerance allowed. 5% loss @ 120 volts is only 6 volts, not enough to affect most common electrical items. Most stuff will tolerate a 10% plus/minus of it's 'nominal' rated voltage, although you usually don't want to see that much for any extended time. I've brought this up multiple times, but I'll bring it up again; VOLTAGE DROP IS NOT EFFECTED BY THE CIRCUIT VOLTAGE. It's calculated strictly from the circuit resistance times the circuit current. So the 120V circuit above with a 5% loss, if it were a 12V circuit with the same resistance and current, the loss is still 6 volts, but now it's a 50% loss. On a 6V system, the loss would be 100%. This is why it's so critical to have adequate wire size and good connections on vehicle wiring. Attaching ground wires. I'll agree that sheet metal screws should never be used. But you don't necessarily need bolted connections; pop rivets can work well for smaller circuits, just don't use the smaller sizes. I'd recommend 1/8" up to 20 amps total connected load, go 3/16" up to 35 amps. Yeah, it'll be a PITA to disconnect it but if it's right you'll probably never have to. Above that, bolted connections will be best. And pay attention to size; even the OEMs up bolt sizes as current goes up (starting circuits typically use at least 5/16" bolts, and alternator output connection are 1/4" or larger) and they're not known for doing more than the minimum. I will mildly disagree with your wire size recommendation for the charging system output. Generators rarely output more than 30 amps, so a #10 will be adequate in nearly all cases. Alternators, you really should do a load calc if you have a lot of electrical loads or if the wire is longer than about 4 feet, particularly if using a 'one wire' alternator. The major flaw with these is they regulate output at the alternator output connection, so any downstream losses (such as would be found in an undersized output wire) will be 'built-in' to your system. 'Three wire' alternators use a 'sense' connection (preferably at the fuse block) to compensate for those losses so that you get full voltage at the block. The larger the alternator output (either type), the more important this becomes.
Anybody have recommendations for the best way to tap into an existing wire for power I'm adding a trailer plug for tail brake and turn and didn't want to use the dreaded scotch locks.
They make T-connectors that plug inline with your existing wiring harness and have a pigtail for your trailer lights. Most auto part stores have them and your local U-Haul will have them.
On a couple of old trucks, the wiring was spliced, taped and generally in bad shape. I fished new wires back to the source under the dash. Made a difference with the extra load of the trailer lights.
Hoping I can get some feedback on this diagram. I put it together from different info that I found here and the web....just want to make sure it is going to work. I have very little to no experience with electrical, so any help will be greatly appreciated. I plan on building my own harness for my '30 roadster project, using cloth/vinyl wiring. The goal is to run everything 12 volts. Flathead engine, 12 volt 4 terminal solenoid and a 1 wire Alternator. BLC headlights, with indicators on top of the headlights, with double contact bulbs. Single fog light up front For turn signal indicator, I plan to use the STAT 700; hence, the addition of the trailer light converter. The rear will have 1157 dual contact bulbs on each side and license plate light. For ignition, I will be using a '32 column drop with push start button. Greatly appreciate any help.
^^^ The trailer converters I have come across have required lights on the upstream side (opposite side filaments act as ground for the internal electronics); wonder if the 700's "warning" light circuitry will provide that or possibly confuse it?
I hate 'whole car' diagrams. Under the best of circumstances on a 30" x 40"sheet they can be hard to read, when shrunk down to 6"x 9" on a computer screen it's impossible. Color-coding is only effective if you're not color-blind and you'd be surprised how many people are. I can't really make out all the detail on the whole diagram, and trying to go back-and-forth between the pieces will give me a headache... What I always strongly recommend to anyone doing their own harness (whether from a kit or scratch) is to break the diagrams into systems and/or circuits. Do ignition/starting as one, lighting as another, etc, etc. Any circuit with a single function and/or single power feed should be shown alone. The only exception that comes to mind is brake/turn/hazard lights, but I'd show these as a system. It's far easier to maintain clarity and avoid mistakes. This is the place to note wire color and size. I also recommend that you number each circuit in conjunction with a 'whole car' routing diagram and incorporate that as a 'legend' on that sheet or a separate sheet. I would also number individual parts of some systems, such as head/front lights and rear lights. Have a reasonable overhead drawing of the car showing main electrical components and actual routing of the wiring bundles/circuits using single lines representing bundles or individual wires, then simply note which systems/circuits are in which bundle or wire. You'll thank me later, and so will any subsequent owners...
I agree, break it down into systems, org even subsystems. It will be so much easier. Sent from my iPhone using The H.A.M.B. mobile app
I have the American Autowire highway 22 kit. I'm not promoting the kit, their website has diagrams for each circuit as Steve is suggesting. Might help you be able to adjust/focus your wiring vision. Phil
Maybe an oversight; but 10 ga won't do for battery cable. You don't mention what you are using for an ign switch; but if you are looking at a Ford column drop switch; it might be a good idea to use it to control a power relay. High beam indicator? Horn relay? Voltmeter ground? Water and oil gauges mechanical? If so, don't need power.
Rich, if not 10 ga then drop to 8 gage? I am using a '32 column drop, like the one in the picture below
The cable between the battery, the cut-off switch, the solenoid, and the starter needs to be bigger; like 1/0 or so. Ground cable too. If your one wire alternator is 100 amp like usual; a step up to 8 ga between it and the solenoid would be a good idea. Ford originally ran only the ign thru the switch; while you don't have a lot of other load; it might not hurt to use a relay to shift it off the switch contacts.
So if I am understanding correctly...break it down something like this, by system. Yes..... With that said, I'll note some things I've noticed.... First, fusing. If you've read this thread from the beginning, you've read me insisting on using correct fuse sizes, particularly not too large. A fuse is there to protect the wire, not the device connected to the circuit. And it's supposed to protect the wire from both short-circuit and overloads. A properly sized fuse will do that. But does every circuit or wire require a fuse? That answer is actually no. So let's talk about why... In the HAMB era, certain circuits as OEM weren't fused. Not because they were too cheap (although that did slightly enter into it), but because one reason was these circuits were inherently 'safe', i.e. if they did fail, it would fail to 'open'. A overload occurs when the connected device starts drawing too much current but still works, even if poorly. A short circuit occurs under one of two conditions; one, the device fails and shorts to ground internally. Or two, the wire is damaged and shorts to ground. There can only be two reasons for the latter; one is poor install, failing to adequately route/protect the wire from physical damage. Or two, accident damage. The OEMs knew this. So the circuits that got fused were the ones that presented a short-circuit hazard, either device or accident caused. As the ignition and starter circuits are both located rather far inside the vehicle, if they sustain accident damage you've got bigger problems than just a short. Lighting is also inherently safe generally, but their location on the easily-crumpled corners means accident damage can be likely, so they get fused. Both your ignition circuit and starter button/solenoid circuits are circuits that fail 'open' and don't need to be fused and never were fused 'back in the day'. I'd actually connect the solenoid circuit to the ignition circuit; the solenoid coil won't draw more than a few amps at most and doesn't need a separate circuit. You can use #16 if you're using any for the solenoid. Use #10 unfused wire to feed the switch, and connect the ignition directly to the switch. Again, this was standard practice. Move the horn circuit from 'ACC' to constant power. This is a safety item and should be available at all times, and this will reduce the load on the ignition switch. If the 'horn button' is a typical steering wheel horn button, I'd highly recommend a relay or you'll be liable to get sparks coming off from under the button. If it's a dash-mount push button, make sure the switch is rated for 20 amps or more. Up the fuse size to 15 amps, 10 seems a bit light for a horn. Anyway, that's what I see.... Hope this helps.
Thank you all for taking your time to look at my diagram and provide feedback....I am very humble and would like to learn everything I can... As I mentioned earlier, I am electrically CLUELESS but doing my best to learn, understand quickly and hoping to put together a good/sound harness for my roadster. I went back to the beginning of the thread, as Steve suggested, and started reading every post.....Glad I did! I think I understand some of this stuff a bit better. If understood correctly, I learned that I have 24.1 amps on the unswitched side, of which 13.6 is the continuous load making 18.4 the total of the unswitched load. On the switched side, I have 28 amps, 16 amps of continuous load and with a total switched load of 28.6 amps Went back to the car and decided I would place the fuse box and battery under the seat, for easy access. Measured my lengths and this is what I ended up with....wire and fuse sizes changed from my original diagram Does it look correct?
Only two things I'd change, and they're minor. One, I'd bump the head/tail/brake/dash light fuses up one size. The wire you have specced is big enough and that will help prevent nuisance tripping if a lamp shorts/burns out. Two, I'd bump the horn wire size up to 14 and use a 15 amp fuse. A horn is technically a 'motor' and can have considerable current inrush when first energized. Other than that, looks good. Great voltage drop numbers; you'll have nice bright lights!
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