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Wiring 101

Discussion in 'The Hokey Ass Message Board' started by Crazy Steve, Nov 5, 2013.

  1. It’s fine as long as everything is infact grounded well, start checking grounds


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  2. blowby
    Joined: Dec 27, 2012
    Posts: 6,857

    blowby
    Member
    from Nicasio Ca

    What happened to Crazy Steve?
     
  3. I am helping my friend wire his car using a Highway 22 kit. The kit has a 175 amp Mega fuse in the lead from the starter to fuse panel and looking on their web sight the newest version of their kit has two 175 Mega fuses the added fuse on the alternator lead. So I suspect these large fuses are being used instead of fusible links as direct short in either lead seems like the only thing that could smoke them.

    Now I have been scratch wiring hot rods for a while, like 50+ years, and I have always wired the main lead direct ( with proper routing and wire protection) with no problem. But considering adding something on my '47. I was looking at maybe using a couple Mega fuses rated closer to the actual load on the main leads (alternator feed would still be direct).

    Some thoughts on either method; or maybe I should just wire the panel direct like usual.
     
    Last edited: Apr 28, 2020
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  4. I'm just finishing up a wiring project now. I wired it from scratch and have a Painless 70 amp Maxi Fuse in the harness between battery and fuse box. I have done it without in the past, but I like the idea of the extra protection. No fuse in the alternator to battery wire.
     
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  5. Halfdozen
    Joined: Mar 8, 2008
    Posts: 606

    Halfdozen
    ALLIANCE MEMBER

    Yeah, me too. But nowadays, a lot of components are common that weren't back in the good ol' days. Things like 100 amp alternators, electric fans, electric fuel pumps, high power ignitions, high power/ draw stereos, power windows, power seats, etc. Much higher current draw needs much bigger grounds.
     
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  6. sub53
    Joined: Jul 22, 2006
    Posts: 4

    sub53
    Member
    from Ma

    I just obtained a beautiful 1965 Ford Country Squire Wagon, a true rust free barn find and redid the ground cable between the engine and the firewall and all the battery cabling and it's pretty impressive how small all this cabling is. It all works for this car. But as a guy who's been working on old cars for over 40 years I'm going to add some hidden grounds underneath the vehicle. It can't hurt, and the older a car gets........

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  7. Rand Man
    Joined: Aug 23, 2004
    Posts: 3,556

    Rand Man
    Member

    I worked with AC circuits for years, but for some reason DC throws me off. Gonna follow this one.
     
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  8. The37Kid
    Joined: Apr 30, 2004
    Posts: 27,326

    The37Kid
    Member

    Has anyone published a how electricity works book on a 4th or 5th grade level?
     
  9. Rand Man
    Joined: Aug 23, 2004
    Posts: 3,556

    Rand Man
    Member

    Electricity is the movement of little bits (called electrons) from a place where there are too many of them, to any place where there are not as many. When you “charge” a battery, you are building up extra electrons on one side. When the battery is “dead”, that means the positive and negative sides are balanced out.

    Nothing is free in this world. A body at rest will remain at rest unless some force causes it to move. That object would keep moving, if it weren’t for some resistance to slow it down. If you roll a ball up a hill and let it go, it will roll back, find a low spot and stop. All forms of energy work this way. Something hot wants to cool down. If you fill a tire with air, it wants to leak out. Electricity is just another form of energy that wants to balance out. We use that movement to do work. We choose a path for the energy to flow (wires). The path needs to have resistance (a light bulb for example) or else you could have trouble called a short circuit.
     
    Last edited: Apr 30, 2020
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  10. As pointed out, your ground wire is too small. Now, how big it needs to be can vary. Too many installers (and aftermarket vendors) treat ground wires as afterthoughts, 'forgetting' that these are in the circuit path and have to be treated and sized just like any power wire. If you're melting a #12, a #10 will likely be too small also.

    Having a common grounding point is actually a good thing, as multiple grounding points can introduce 'weirdness' into a system all too easily. But before everyone starts installing oversized ground wires, keep in mind that if grounding to the chassis/body, these can be considered as a single point as long as they're electrically continuous, i.e. close to zero ohms between any two points. I'd highly recommend 'bonding' the chassis/body/motor to each other. Large braided ground straps are commonly available for this. But if you are going to use separate ground wires, at a minimum you must size it for the total connected load; no guesses here. If as an example you're grounding six circuits that draw ten amps each (and could all be continuously on for more than 3-4 minutes at a time), the ground has to be sized for a 60 amp load. Too small and you'll get excessive voltage drop, and that drop is converted to heat. Poor connections can contribute to this also. I would also avoid putting too many connections on a single stud. A small buss bar would be better; a small piece of 3/16" aluminum plate drilled/tapped for screw connections should be adequate.

    If you have intermittent loads (such as turn signals, horn, or cigar lighter) that are on only momentarily you don't have to add all of these in but I would strongly recommend adding in the largest of these to the total to reduce voltage drop to the other circuits, otherwise you may have issues. This can be a judgement call, but I'd err onto the larger wire side.
     
    Last edited: May 2, 2020
  11. Halfdozen
    Joined: Mar 8, 2008
    Posts: 606

    Halfdozen
    ALLIANCE MEMBER

    A friend has a 'glass '34 three window with a serious 383 sbc, he had chronic high rpm miss problems until he ran a braided ground strap from each cylinder head to the chassis- problem solved. Spark plugs and high voltage ignitions need good grounds too.
    I've seen enough problems with residential wiring where aluminum and copper were joined, any time I attach a copper terminal to an aluminum part in a car I use a dab of Noalox. Cheap insurance.
     
  12. olscrounger
    Joined: Feb 23, 2008
    Posts: 3,976

    olscrounger
    ALLIANCE MEMBER

    Have wired many cars over the years. Was a lineman as well. Had a weird one a few days ago. Wife's 55 I rewired 20 years ago-never a problem. Started it up and it ran fine-drove it around a bit and then saw 11 volts on the voltmeter in the car. Checked alt and batt post 13.5 volts. Inside car 11 volts at panel etc! OK -bad connection. Well pulled wire that feeds panel from starter lug into car and cut at firewall. Cut it all apart-saw nothing,all connectors looked good too and ohmed out fine.Dropped fuse panel suspecting loose/bad connection-nothing-not loose at starter lug either. Made a new loom all the way from the stater lug to the panel. All good! Still a bit baffled. It was a #10 and #8 is all I had so that works. Realize it ran this way for 20 years no problem. There is no heavy load thru the panel.
     
  13. I would never attach copper to any raw aluminum, even with antioxidant. Use a tinned copper crimp lug instead; that's why they're tinned.
     
  14. Halfdozen
    Joined: Mar 8, 2008
    Posts: 606

    Halfdozen
    ALLIANCE MEMBER

    Yup, I use tinned lugs and terminals, still use antioxidant. Prefer brass or stainless for ground busses, the boat guys have some nice components.
     
  15. blowby
    Joined: Dec 27, 2012
    Posts: 6,857

    blowby
    Member
    from Nicasio Ca

    Just want to make sure: My DVMs, one good one and 50 HF freebies I am gradually tossing out, all read about an ohm of resistance just touching the probes together. So I subtract that amount from whatever I am measuring, correct?
     
  16. Blues4U
    Joined: Oct 1, 2015
    Posts: 4,866

    Blues4U
    Member
    from So Cal

    FYI, no regular DMM are very accurate reading ohms at or below 1 ohm, they just aren't. High accuracy measuring very low ohms requires a special ohm meter, they're quite expensive for auto use.
     
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  17. Yes, but that still won't guarantee that you'll have accuracy at low ohm values. I've had multiple cheapo HF meters, most were off at least some, although I did have one that seemed to match my expensive Fluke... until it didn't... LOL.

    Now, FWIW my Fluke seems to meet it's advertised spec of resolution down to .1 ohm, or at least it did the last time I checked it against a known resistance. Meter performance can degrade over time, what with dirty contacts and whatnot. But even so, very small ohm values (at or below most hand-held meters resolution) can show up as a pretty large drop on our 12V systems (and even more so in a 6V one). So checking for circuit resistance/continuity has limited utility for troubleshooting. I'm not saying you shouldn't do it, as this is the preferred method for searching for gross issues or verifying that you actually have a complete circuit before applying power. This can prevent letting the smoke out...

    But if after doing a ohm/continuity test, applying power and you still have issues, now what? Do a direct-read voltage drop test. Performed while energized and preferably under full load, this will give a real-time indication of where your problem is. The procedure is laid out here:
    https://www.jalopyjournal.com/forum...rcharged-battery.1192632/page-2#post-13566360
    Generally, even the cheapo meters will read to at least .01 volt accuracy, so this will nearly always show the problem.
     
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  18. Boneyard51
    Joined: Dec 10, 2017
    Posts: 4,330

    Boneyard51
    Member

    Ok, Steve, here we go again! Lol. I have always adhered to the statement “ you cannot have too many grounds” and have stated it , often. I have added grounds before on equipment that seemed to be not getting a complete circuit. On all the trucks I outfitted with auxiliary 12 volt power equipment, we added a designated ground. Usually a 0 cable, from the battery ground to the frame to give a large path for the high amp draw! This solved some problems we were encountering.
    Is there a problem with “ too many grounds” ? Thanks










    Bones
     
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  19. JUSTIN PERSINGER
    Joined: Apr 28, 2020
    Posts: 95

    JUSTIN PERSINGER
    Member

    DC is just straight direct current, it does not use the alternating sign wave like AC. So DC is pretty much wired with a Hot wire and a Common or Ground.
    Just use Ohms law and Kirschoffs law as applied and it should go pretty smooth.

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  20. JUSTIN PERSINGER
    Joined: Apr 28, 2020
    Posts: 95

    JUSTIN PERSINGER
    Member

    That is voltage drop from the battery to the guage. Rewire it with a closer voltage supply and it's own good ground. See if this improves the volts.

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  21. Boneyard51
    Joined: Dec 10, 2017
    Posts: 4,330

    Boneyard51
    Member

    Rand Man, I’m right the opposite! Lol Having worked on DC circuits most of my life, I have a problem with AC electricity! Funny!








    Bones
     
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  22. Grounding is the least-understood part of electrical engineering. During all my years in the trade, every time the NEC was revised, there was always changes to grounding. Stuff that was required changed to being banned, and vice-versa sometimes. Most changes were the result of 'field testing', i.e. they found out it didn't always work... LOL

    The real key to good grounding in a vehicle is making sure that however many ground points you have they are A. electrically continuous to each other and B. have zero or very close to zero ohms differences between any/all points.

    As a practical matter, what this means is you need to be careful about grounding means. If you've bonded the frame/body/motor/running gear properly, attaching a ground to any metal part will be acceptable. This is the best way, as it makes troubleshooting issues generally much easier to track down and reduces the size of the ground wire. The problem here is fully-detailed painted/powdercoated parts can interfere in proper metal-to-metal contact.

    What I would avoid is installing a limited number of 'ground points' to that same structure and making multiple attachments to those points. This can create 'hot spots' that can cause stray currents to interact between the points, sometimes introducing 'weirdness' into the system. This is more of an issue as total grounding current load at that point goes up. Remember, electricity always seeks the path of least resistance. I'm not saying this will happen, just that it can...

    Of course, you can always use a single grounding point and eliminate all these issues, but this introduces issues of it's own. Pulling all grounds back to a single point means circuit length increases, which will require larger wire to keep voltage drop low, plus you're going to have a 'busy' connection point. This is an issue on 'glass cars where it's nearly required, not something I'd recommend for a steel car.

    That's technically not true. With the exception of the purely resistive loads like lighting, cigar lighter, and probably most gauges, pretty much everything else in a vehicle uses AC principles to operate. While as a practical matter this can generally be ignored, not always; motor circuits in particular need to be calculated for proper size.
     
  23. Rand Man
    Joined: Aug 23, 2004
    Posts: 3,556

    Rand Man
    Member

    I don’t know why, but sometimes car wiring throws me off. I know the laws of don’t change. I’m just used to seeing all the wires involved in the circuit. Most of car electrical gremlins I’ve chased have been a bad ground.

    Makes sense when I think about it. Every circuit needs to be complete to “work” properly. If the path is broken (called on open circuit) the electrons cannot flow back to the other side of the source. You could say an incomplete open circuit has “infinite” resistance. A dirty terminal could cause a bad ground, meaning the path has higher resistance than the intended design, so it won’t work properly.
     
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  24. JUSTIN PERSINGER
    Joined: Apr 28, 2020
    Posts: 95

    JUSTIN PERSINGER
    Member

    I agree, I was just trying to keep it as simple as possible. Calculating amperage, resistance, wire length motor loads and etc can get overwhelming to a beginner. Plus, when you get into sensors with a 0v reference signal, 5V positive, or get into thermocouples that output mV and have to convert them to temperature readings. There is a lot more than just a hot and common, but for most aftermarket wiring harnesses the math is already done.

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  25. To be honest, I've seen very few aftermarket harnesses that I would personally buy...

    They generally mimic the OEMs (who usually cut every corner they can), and throw in at least a few more marginal items for good measure IMO.
     
  26. Boneyard51
    Joined: Dec 10, 2017
    Posts: 4,330

    Boneyard51
    Member

    Ok, Steve, you lost me on some terminology! What does “ electrically continuous to each other” mean? Any time I added a ground I made it large and made sure the frame, usually where I was adding grounds ,was very clean. I would usually hit it with a four inch grinder. Then after tightening it real tight, I would cover it in a coat of paint.


    Oh, And, by the way, glad your back!!!







    Bones
     
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  27. That's just a way of saying that each part of the vehicle that you use for a ground point is connected electrically to every other part that may be used as a ground point, so that on an electrical basis, it's all one part. So that even if you pick the two points furthest apart to test between, you'll still get a very low ohm reading (.2 ohm or less, preferably less).
     
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  28. Blues4U
    Joined: Oct 1, 2015
    Posts: 4,866

    Blues4U
    Member
    from So Cal

    Working with guitar amps (which use both AC & DC), grounding is a real big issue. A lot of noise can be generated in an amp due to poorly thought out grounding. There are several schools of thought for this. One popular method for hand wired amps is what's known as "star grounding", where all the grounds are brought back to a single point on the chassis. Another method, less common, is using a buss bar. Grounds are connected to the buss sequentially, as they exist in the signal path. Probably the most common method is to group the grounds together by their function. What you certainly don't want to do is to just attach the grounds haphazardly all over the chassis wherever is convenient, that is a sure method of inducing a ground loop and adding hum. I doubt any of this applies to hot rods, though in OT cars with more sensitive electronics is might be a concern.
     
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