We always here about voltage drop in the classes we go to but does it ever really apply to fixing cars? It is always taught but never really shown in real life examples. Well any one who watches my channel knows I have shown in several videos why it is so important and how to use your meter to see the "pressure" difference between two points. Hear yet again is another example.
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49 thoughts on “Voltage drop, do we really need to know it!?”
  1. Avataaar/Circle Created with python_avatars Paul C Townsend says:


  2. Avataaar/Circle Created with python_avatars wolf north says:

    should you disconnect the negtive post of the battery while you are working on the positive side of the battery?

  3. Avataaar/Circle Created with python_avatars Ken Smith says:

    What do you think of the LoadPro for this application?

  4. Avataaar/Circle Created with python_avatars Dependable Auto Truck says:

    these reminders are so good glad you took the time to show

  5. Avataaar/Circle Created with python_avatars LetItGrowDad says:

    This guy needs to do schooling , love to have as a teacher ! 👍👍👍

  6. Avataaar/Circle Created with python_avatars ozzman530 says:

    I just found this channel, pure gold the way you analyze the facts with a meter instead of throwing parts or using a simple jumper. Quick question, based on the comment about heat and resistance. How hot should an alternator get? I know its on an engine but most times there is air flow around an alternator. Should it be too hot to touch under normal circumstances or would that be an indication of an issue?

  7. Avataaar/Circle Created with python_avatars Peter Maciak says:

    What about grease on terminals and connection points. Is that just a tale from the olden days or is there some validity to it. I was told that dielectric grease on terminals will eliminate the potential for this sort of issue. Same with connection points, clean and a tad of grease will keep the connection point from crusting up .

  8. Avataaar/Circle Created with python_avatars Coy Carlson says:

    All the stuff South Main Auto demonstrates / teaches is GREAT STUFF 👍😊 YOU have many , many years of PROVEN EXPERIENCE and vehicle repair knowledge and when I watch you make repairs and you say – if I can do it – you can do it – I'm STOKED 😊 Again – GREAT INSTRUCTION , I learn something from every video you make – MANY , MANY THANKS and , no doubt , if I lived near you – I would surely bring my vehicles to your shop for repair and ABSOLUTELY REST ASSURED – knowing you would repair it properly. ✌️✌️✌️

  9. Avataaar/Circle Created with python_avatars Bob DePlachett says:

    Can fluid leaks, say from a bad O ring on a coolant line to the radiator, affect wire grounds or wire connections? BD

  10. Avataaar/Circle Created with python_avatars boostedsil40 says:

    can i create a load in a circuit for somthing like starter that doesn't have current flow with a lightbulb? could i hook a light in the circuit so it can be tested?
    i understand a light will only draw around a few amps but if you have a voltage drop in the wire wouldnt it i be able to see it via creating a load with light so i can voltage drop test? or a cheap way to load up the circuit so i can perform the test.

  11. Avataaar/Circle Created with python_avatars NICk AYIVOR says:

    Good Morning South Main Auto Repair
    Thanks 👍
    From Nick Ayivor from London England UK 🇬🇧

  12. Avataaar/Circle Created with python_avatars John Casor says:

    now really this should be called a resistant test on voltage ??? meaning lack of voltage getting through the cables or connections??? and it could be called a voltage loss ??? but not really a loss,,, because the voltage is not really loss,,, it is there but not getting through to the other side, remember this: ( Most Electrical problems are resistant by nature and occur at connections ),,, My College Teacher made the whole class say this at the start of every class for 2 years… i think he was a great teacher 27 years he taught in a college…

  13. Avataaar/Circle Created with python_avatars John Casor says:

    Another Great Video…

  14. Avataaar/Circle Created with python_avatars Emik says:

    Just want to say thank you for sharing your knowledge. God bless you

  15. Avataaar/Circle Created with python_avatars AJ096 says:

    Great information. I am studying for ASE certification and on the study guide I’m learning about voltage drop. This brings me to a question. I noticed that you connected the meter leads to the source in question and then cranked the engine, read the meter, and stoped cranking. My question or confusion is that the ASE study guide says to remove the lead from the battery post before you stop cranking the engine to avoid damaging the meter. I see that you did not do that. Is it even necessary to do so in that case?

  16. Avataaar/Circle Created with python_avatars John Thake says:

    Can any one help me understand voltage drop I don’t understand the multimeter readings what you should be reading on the meter when testing for a voltage drop but I understand what is meant by a voltage drop when something is not working

  17. Avataaar/Circle Created with python_avatars DormantIdeas NIQ says:

    Even if not knowing anything about electrical connections, as in the invisible film that forms between a battery post and its terminal that will keep a battery from delivering the power, it befalls me that an idiot who replaces a battery would not automatically clean ALL connections to shiny metal!!! period. idiots! but then one should do that before replacing the battery and avoid to buy a new battery that is not needed.

  18. Avataaar/Circle Created with python_avatars fernando13e says:

    Great explanation on Voltage drops.. I'm having a real world situation right now, it's a 93 Ford Ranger with the 3.0L V6, with ignition off I have around 13v, ignition On (on run position) drops down to 9v I try to crank it and no joy, put an amp meter in series with the negative cable and battery post and I'm looking at 4.5amp draw mainly because the FP is on all the time, but still having 9v with ignition on, any suggestions?.

  19. Avataaar/Circle Created with python_avatars Scott Tucker says:

    258000 miles on a northern car,I thought all those northern car rusted and fell apart right after 100000 miles
    But love your Channel keep up the good work and yeah you might make a good teacher probably easier on that old back and more money

  20. Avataaar/Circle Created with python_avatars Ronald Bergeron says:

    Great video. Thank you Eric. Measuring the temperature is a great ideal.

  21. Avataaar/Circle Created with python_avatars John Guarnieri says:

    Great video I just wish you would mention what the readings you are finding should be, for instance, you should see no more than .5v voltage drop on the ground side or the positive side

  22. Avataaar/Circle Created with python_avatars Jolliver Mediana says:

    So… The voltage drop from the positive cable clamp to the positive battery post must be equal to 0V? Why?

  23. Avataaar/Circle Created with python_avatars Ivan Olsen says:

    one of the first things I was told / learnt as a 17 yr old was battery terminal corrosion … barcbonate of soda in solution pour over dismantled parts is a solution … or was that baking soda

  24. Avataaar/Circle Created with python_avatars DELLISTX says:


  25. Avataaar/Circle Created with python_avatars Brian Mohns says:

    Good explanation there Eric. Thanks

  26. Avataaar/Circle Created with python_avatars DrGreenThumb420 says:

    Even a blind technician at Wal-Mart could have seen the dirty cable was an issue

  27. Avataaar/Circle Created with python_avatars orian cunningham says:

    so someone really took those terminals off to replace both batteries, and changed a starter and didn't once think to maybe clean the terminals? wild.

  28. Avataaar/Circle Created with python_avatars Greg Hamilton says:

    Great job. Maybe I can find out why I keep getting a PO562 code on my PT Cruiser!

  29. Avataaar/Circle Created with python_avatars Alan Torrance says:

    On starting engine after fixing battery problem the Engine Light was on. Other problems.

  30. Avataaar/Circle Created with python_avatars Paul Schenkel says:

    All the connections need to be replaced.

  31. Avataaar/Circle Created with python_avatars Lucas Theriault says:

    Just subbed your videos are a wealth of knowledge. I just picked up an 07 nbs silverado and I got it dirt cheap has been to several shops with no improvement for the previous owner no communication between any modules with blue driver scan tool drove it home with only 1st 2nd 3rd gear it slammed every gear when shifting, terminating resistor checked out at 120 ohm I was at a loss ended up pulling both fuses for the abs and got communication back with all modules except the abs module of course but when I put the fuses back in I got communication with the abs module but I get codes for all the wheel speed sensor circuits I'm at a loss now I have to check all the wires I guess before I condemn the abs module itself still doing research for that.

  32. Avataaar/Circle Created with python_avatars Michael Knorr says:

    Jumpers go around the issues to start. A voltage drop will locate the issue so that you can replace a failed part.

  33. Avataaar/Circle Created with python_avatars Rafael Marin says:

    Thank you SMA.

  34. Avataaar/Circle Created with python_avatars Dennis Marble says:

    Another great job explaining voltage drop testing. Keep making these videos!

  35. Avataaar/Circle Created with python_avatars konstantinus Stoyanov says:

    Nice, video is great

  36. Avataaar/Circle Created with python_avatars J S says:

    This maybe a dumb question, but could you ohm these connections out to find these problems? Or is the voltage drop check the best way to find these bad connections?

  37. Avataaar/Circle Created with python_avatars D Veloso says:

    Have question regarding voltage drop.
    scenario 1.
    Objective=To check the integrity of ground wires from the PCM.
    -KOEOff ( reading 5 volts on ref) – circuit is on ( supposedly loaded)
    hook up one lead to BAT (Neg)and the other lead to entry point at PCM connector ( connector is attached to PCM).
    DMM reads 6.2mV.
    Would such procedure establish if the circuit is good ( mainly to see if wire going into PCM is connected to ground and in good condition)

    Can the LoadPro also perform this test, if so what are the conditions and hook up.

    Someone suggested to disconnect PCM wire, use a test light. One side goes to BAT+ the other touch the ground PCM wire, if light is "bright" circuit OK.
    I ask that you comment on the merits or lack thereof of each method, if possible
    Thank you

  38. Avataaar/Circle Created with python_avatars WouterB76 says:

    Yeah, just throw the parts cannon at it with a blindfold on….luckely there are still mechanics like Mr O around.

  39. Avataaar/Circle Created with python_avatars Adam Kapraun says:

    Is it possible to connect the starter test button alligator clips to the positive and negative wires that connect into the battery fuse terminal that is connected to the battery positive post. This meaning, is it possible to disconnect the positive and negative starter wires from the fuse terminal block(the fuse terminal block is connected onto the positive post of the battery), and then attach the starter test button on the positive and negative wires? My vehicle is a Honda HR-V 2017 EX-L FWD. Thank you in advance for ready my comment.

  40. Avataaar/Circle Created with python_avatars Adam Kapraun says:

    I love your way of explaining your approach. Clear and to the point. I also appreciate you using a diagram. Great work! Subscribed and liked!

  41. Avataaar/Circle Created with python_avatars Daniel Woodhouse says:

    Really good explanation thanks! Especially good for me as I am doing an apprenticeship and this was a good video to learn voltage drop from.