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Wiring 101

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

  1. blowby
    Joined: Dec 27, 2012
    Posts: 7,513

    blowby
    Member
    from Nicasio Ca

    Thanks. Is voltage difference from one end of a wire to to the other a good indicator of correct or incorrect wire gauge? Or can resistance be measured under load?
     
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 48,679

    squirrel
    Member

    Yes, you can measure the voltage drop, and that will give you an idea of how well the wire is sized for the load.

    An ohm meter measures resistance by measuring the voltage drop under a controlled load. The meter applies a voltage, and measures the voltage drop. It displays the voltage drop as resistance (Ohms). You won't get an accurate reading if there is a load on the wire, in addition to the load the meter provides.

    You can also use an ammeter to determine what the load is. An ammeter is connected in line with the load, the current flowing through the ammeter is the current of the load. If you find it's a 30 amp load, then you probably want to use 10 gauge wire, although 12 will probably work under some conditions.

    Also, the longer the wire, the higher the resistance. The smaller the wire, the higher the resistance. There are online calculators to help you figure out what the resistance of a wire will be, based on gauge and length.
     
  3. Halfdozen
    Joined: Mar 8, 2008
    Posts: 620

    Halfdozen
    ALLIANCE MEMBER

    On the subject of GM starter solenoids:
    I've been laying out a system for my car lately, sourcing components, etc., and I stumbled across this-

    This man says some GM solenoids can draw as much as 40 amps, that in the '70's the factory upgraded from 14 to 10 gauge wire for the solenoid coil. He says the 14 gauge wire contributed to typical GM hot start issues.
    It's a convincing video, I'll be following his suggestion to use 10 gauge and a relay to operate the solenoid.
     
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  4. TrailerTrashToo
    Joined: Jun 20, 2018
    Posts: 949

    TrailerTrashToo
    ALLIANCE MEMBER

    That cube relay, as shown in the video, is typically rated at 30 Amps. You might be creating a different reliability issue.

    My International Harvester SV392 engines used this type of Delco starter. I went the over-kill route and used a 1960's Ford starter relay.

    https://www.autozone.com/batteries-.../relay-starter/duralast-relay-f496/118604_0_0
     
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  5. Maybe... it depends on how big the difference is. Now as to measuring wire resistance in an automotive harness, don't even try. Even the smallest wire size used has a lower resistance than what the typical hand-held meter can resolve. You can measure circuit resistance, which includes all connections, but that still may not show up problems, merely indicate that you do have a circuit. You can't measure resistance when the circuit is energized.

    Here's a tutorial on checking with a VOM... Technical - How to Use a Multi-meter | The H.A.M.B. (jalopyjournal.com)

    Checking circuits 'cold' (deenergized) will only show up fairly gross issues, but should be done on any new harness or modified circuits to 'prove' that the connections go where they're supposed to. To get accurate voltage drop readings, you have to check with the circuit under its load, and the readout will be in volts. Generally speaking, a drop of more than 5% should be avoided. The lower the better...
     
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  6. That wouldn't surprise me in the least. That solenoid is actually a linear motor, and has current inrush just like any other motor. I'll agree with trailer Trash, use a Ford starter solenoid rather than a cube relay for reliability. Jumper the solenoid connection directly to the battery connection on the starter.
     
    loudbang likes this.
  7. Halfdozen
    Joined: Mar 8, 2008
    Posts: 620

    Halfdozen
    ALLIANCE MEMBER

  8. For $26, I'd buy a plain ol' Ford starter solenoid for $15....

    Now, for use as a relay for switching the switched half of a fuse panel, this would be perfect.
     
    LWEL9226 likes this.
  9. TrailerTrashToo
    Joined: Jun 20, 2018
    Posts: 949

    TrailerTrashToo
    ALLIANCE MEMBER

    The problem is finding a replacement in Rattlesnake Crossing, TX. From the link above, the lead time is 16 days.

    "Waytek Part #: 75150
    MFG Part #: 05903300

    In Stock: 21 pcs
    Qty On Order: 0 pcs

    Standard Lead Time: 16 Days"
     
  10. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 1,902

    ekimneirbo
    Member
    from Brooks Ky

    Battery Question.......I purchased a new Interstate battery last year (2019) in September. After a while it went dead, so I charged it with a Smart Charger and all was well for a while. It went dead a couple more times and then I realized what was causing it, or at least contributing to it. I had a couple of those little charging cords plugged in and they had lights at the plug in that stayed on. It was under the dash at a point where you could not see the lites. I disconnected them and recharged the battery again. Things went well for a while as long as I drove the vehicle regularly and it got charged. If I let it sit for several (4 or more) days, it would go dead again. Thinking that the fact it had been run down several times before I discovered what I thought was the problem, I figured the battery was just damaged internally and would never hold a charge well. Since its still in warranty, I returned it to Costco and they courtesously provided a replacement. I'm thinking to myself that this battery may have been sitting for some time, so I touched the two leads from my handy dandy battery tester and it showed the battery was up to snuff.....or at least acceptable. I decided to hook my Smart Charger up and see what it said ......and be sure I start out with a fully charged battery. The Smart Charger went thru its analysis procedure and then showed the battery at about 30% of charge. I left and took the wife to get a burger and came back about an hour later. The Smart charger said the battery was at about 90% charge .

    So, is that normal for a new battery ? :oops:
     
  11. Halfdozen
    Joined: Mar 8, 2008
    Posts: 620

    Halfdozen
    ALLIANCE MEMBER

    I will be using one of the Littlefuse relays for my switched panel.
    I think I'll also use a Ford top post solenoid mounted along side my GM solenoid on the motor. Easier to package, takes less room than the side post version. Thanks to TTT and Steve for the idea.
     
  12. I'd say no, but these days you can have no idea how long a battery has been sitting on a shelf. Once acid has been put in, it starts the march to inevitable failure. I can remember when batteries were shipped dry and activated only upon purchase. The problem here was not all sellers did that right, so the practice disappeared. The other issue is drains. Back in the day, the only drain cars had was a electric clock if so equipped, and many of those weren't constant, but intermittent; the spring would wind down, the motor would rewind the spring then shut off until next time the spring needed winding.

    Constant drains are worse. Even a small one can suck a battery down given enough time. This is where Amp-hour ratings come in. They're supposed to tell you how long in hours the battery can deliver 1 amp continuously, a smaller drain amount will extend the time but there is a finite limit. But 4 days is not long enough unless that's a pretty serious drain.

    Have you disconnected the battery and then checked it after 4-5 days? If it's still going dead, there's an internal problem.
     
  13. Blues4U
    Joined: Oct 1, 2015
    Posts: 5,560

    Blues4U
    Member
    from So Cal

    25+ years ago the standard practice with a brand new battery was to always put it on a charger for awhile before installing it. Whether it was a dry battery that we put acid in, or a wet battery. I've always followed that practice since then
     
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  14. blowby
    Joined: Dec 27, 2012
    Posts: 7,513

    blowby
    Member
    from Nicasio Ca

    I have a brass connector inside a rubber boot that does not come apart. I can see the brass is corroded and green inside. Is there something I can soak the whole thing in to get the brass clean again?
     
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  15. Halfdozen
    Joined: Mar 8, 2008
    Posts: 620

    Halfdozen
    ALLIANCE MEMBER

    I'd try citric acid first.
     
  16. FOURTYDLX
    Joined: Feb 22, 2006
    Posts: 718

    FOURTYDLX
    Member

    Baking soda and water ,small acid brush than flush with water
     
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  17. Boneyard51
    Joined: Dec 10, 2017
    Posts: 4,935

    Boneyard51
    Member

    Arm and Hammer baking soda with a little water and a brush, then rinse off.It will look like new. Be careful of where the rinse goes, as it is corrosive. I usually do it out side in the gravel and rinse real good.






    Bones
     
  18. blowby
    Joined: Dec 27, 2012
    Posts: 7,513

    blowby
    Member
    from Nicasio Ca

    Thanks guys. Someone suggested vinegar, which I already had, so I tried it on a test piece. Sorry no before picture, it was black. 20210103_121827_resized.jpg
     
    Halfdozen likes this.
  19. Maicobreako
    Joined: Jun 25, 2018
    Posts: 127

    Maicobreako
    Member

    Very informative thread!
    I scarfed a fuse panel out of a junked modern Jap PU, there's #10 and #12 wires coming in, but going out it's mostly #18 and a few 16s. The smaller wires come off 10, 15, and 20 amp fuses. How can those small wires carry those loads?
     
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  20. TrailerTrashToo
    Joined: Jun 20, 2018
    Posts: 949

    TrailerTrashToo
    ALLIANCE MEMBER

    Very, very carefully.

    The job of the fuse is to protect the wire from melting. In most cases, the actual load (measured in Amps) is a less that the designated fuse Amp rating.

    Add to this, the "bean-counters" are looking for cost reductions and almost everyone is looking for weight reductions (i.e. better MPG). The end result is specifying the next smaller wire gauge and crossing your fingers...

    Case in point. About 45 years ago, I finally was able to buy a good used Datsun pickup as my commuter vehicle. On night, on my way back from night school, the headlights went out. Fortunately, I was on country roads, almost home - turned on the 4 way flashers and got home. Next morning, found a blown blade fuse (never seen one before, all my old junk had glass tube fuses). Went into the Datsun dealer for a fuse in the morning. Parts guy said that blowing the headlight fuse was a common problem, the factory had undersized the headlight circuit. He handed me a 5 amp bigger fuse and I never had any more problems.

    p.s. in 1979, I moved to Arizona and traded this for a 1932/1933/1934 Ford 2 door channeled "hot rod". It really was too crude to be a "Street Rod" - "Rat Rods" had not been invented yet - I called it a "Shot Rod".
     
  21. FOURTYDLX
    Joined: Feb 22, 2006
    Posts: 718

    FOURTYDLX
    Member

    I install a circuit breaker on headline circuit
     
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  22. curiousart
    Joined: Oct 4, 2006
    Posts: 4

    curiousart

    Any of the Forrest Mims books are great for someone looking to understand this stuff. Low on the maths, lots of cartoons. What will really help stuff to sink in is to actually build a few of the very simple projects---that's what helps this stuff come to life in your head as knowledge, and not just dry theory. Go blow up some components, and have fun!
    https://www.amazon.com/Getting-Started-Electronics-Forrest-Mims/dp/0945053282

    Also, the "Basic Electricity" and "Basic Electronics" published by Rider in the early 50s are very beginner friendly. Same deal, lots of cartoons and easy math.
     
  23. Boneyard51
    Joined: Dec 10, 2017
    Posts: 4,935

    Boneyard51
    Member

    They really can’t do it very good. Most OEMs use small wire. You should replace the wire , if possible or replace the fuse panel all together!






    Bones
     
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  24. blowby
    Joined: Dec 27, 2012
    Posts: 7,513

    blowby
    Member
    from Nicasio Ca

    I'm looking at buying a clam on meter, like this. What can these do on DC, can they measure amperage or voltage just by putting the clamp around a wire? Seems like that's more of an AC thing.

    [​IMG]
     
  25. Rand Man
    Joined: Aug 23, 2004
    Posts: 3,820

    Rand Man
    Member

    The clamp-in function is to measure current flow (amperage). The laws of physics on that work the same, AC or DC. The movement of electrons in a conductor creates a magnetic field. That tool will measure the field strength and read out in amps. It should have lead wires you plug in, to measure AC/DC Volts and Ohms or resistance.
     
  26. Blues4U
    Joined: Oct 1, 2015
    Posts: 5,560

    Blues4U
    Member
    from So Cal

    I only see an AC function for amps, AC/DC for Volts, and and Ohms setting, but no DC Amps
     
  27. Rand Man
    Joined: Aug 23, 2004
    Posts: 3,820

    Rand Man
    Member

    You could be right. I’m not familiar with that model. I’m pretty sure the Amprobe brand, analog meter will measure DC amperage. It’s been years since I’ve used mine. It is really a simple device. The magnetic field around the wire induces electron flow in the jaws. That flow induces a field in the little coil that makes the needle move.
     
  28. That's a pretty expensive tool for as often as you'll need it (and this one doesn't do DC current). If you're getting into the weeds on a late-model with electronic everything you may need the capability but for our cars something like this is really all you need....
    Tool Aid 24600 600 Amp Alt-Gen-Start Ind., Price/EACH Sale, Reviews. - Opentip
    ... for a fraction of the price.
     
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  29. blowby
    Joined: Dec 27, 2012
    Posts: 7,513

    blowby
    Member
    from Nicasio Ca

    I can't tell how that hooks up, hard wired? I have a cheaper version of the one I posted, but it too doesn't do DC current without using the test leads. Was just wondering if there was a version that did DC without opening up the circuit.

    My off grid solar system has a DC current meter with the positive wire passing through a hole (I forget the name of that dingus), but it has a ground wire going to the battery.
     
  30. Nope, there's two slots in the back, a big one for high amps and a small one for lesser amounts. Simply slip the wire into the slot, no direct connection.
     

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