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1G [RESOLVED]Entire Chassis showing voltage?

Posted by a7xinsane, Sep 5, 2019

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  1. a7xinsane

    a7xinsane Proven Member

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    I started a thread about an idle surge issue I was having and while it is not resolved this has become a bigger problem. Started with me wondering why i had 4 - ways but no turn signal so i replaced the multi function switch. No go. Started doing some wire following and touched a ground with my probe and it was showing a constant voltage reading... depending on which ground or where at on the body you probe the voltage varies between .4 to 2.3 volts. Pulled motor, trans, entire interior ( dash/seats/carpet/door panels/ you name it) and unplugged every connector one by one and tested ground. Still voltage... I have unplugged literally everything and have the entire wiring of the car laid out on the shop floor cut open and I can not see ANYTHING wrong. no shorts, corrosion, or bad plugs. I am at a complete loss. If it wasnt for the money already invested in this project and the stakes other than that I would burn this thing...
     
  2. Mello

    Mello Proven Member

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    If there is any resistance in the current path you will have a small voltage potential. Measure the resistance along with the voltage & you will see that the resistance will be different at the different grounds. Ohms laws i=v/r or v=i*r. Run larger ground wires if you want smaller voltages at the grounds.
     
    Last edited: Sep 6, 2019
  3. ThunderChild

    ThunderChild Supporting VIP

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    Or get yourself a better DVOM...
     

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  4. luv2rallye

    luv2rallye DSM Wiseman

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    Where do you have the voltmeters negative lead? It must be connected directly on battery negative to be absolutely sure and get the true voltage reading (try that first as a test). If you connected it to chassis/body (assuming it's the same) and you have some current flowing through a resistance between battery negative (example: poor negative battery terminal connection or poor battery negative to chassis/body connection) and where you connected it, then you will see a voltage (which is then misleading - you're just seeing a voltage drop caused by current flowing through a resistance).
     

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  5. a7xinsane

    a7xinsane Proven Member

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    Using a snap on power probe type device in conjunction with a fluke multimeter to verify my voltage readings. it will read voltage if you touch the negative lead to the negative battery terminal and the positive to the chassis at any point there is at least .5 volts showing on my fluke multimeter.
     
  6. rabenne

    rabenne Proven Member

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    +1 luv2rallye

    Do you know how to properly use that power probe? I watched a guy tell me he had positive voltage on a AC clutch wire for 2 hours before I mentioned to him he had the battery ground disconnected... I mean no offense, I just worry that you may be going down a pitfall rabbit hole.

    Since you have that and a fluke dmm, I would recommend whichever you are most comfortable with.
     

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  7. a7xinsane

    a7xinsane Proven Member

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    I'll take a pic of it when i get back. I do this professionally for a living but i understand the skepticism
     
  8. luv2rallye

    luv2rallye DSM Wiseman

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    It's not that uncommon to see a 0.5v voltage drop along a ground path when enough current is flowing. All ground paths have some resistance especially at connection points like battery terminals and chassis points. So enough current flowing and you will see a voltage drop across it. Even 0.1 ohm resistance in starter cable connections will prevent a starter from working since there is so much current flowing there (voltage drop V = I x R) - that's why many people incorrectly replace the starter or battery when the real problem is the poor cable connection. It's important to have battery/starter cable/terminal connections corrosion/crud free and tight. Also the more separate ground connections from devices the better (and battery negative to chassis/body AND battery negative to starter mounting bolt should be SEPARATE large cables). Perhaps one of your major ground connections isn't making a good connection. You can also disconnect the battery (with engine off) to measure resistance across cables/connections (so no current is flowing to eliminate voltage drops). Although if you know what you are doing, it's easier to find the high resistance cables/connections by measuring voltage drops across them (literally putting the voltmeter probes across suspected high resistance cable/connections when current is flowing to check how much voltage drop there is).
     

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  9. a7xinsane

    a7xinsane Proven Member

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    it is only the lighting harness that causes this short. with the fused connection and starter connection hooked up i get good ground everywhere. its only when i put the lighting ring on that it starts putting voltage through the chassis so i know my problem has to be somewhere in that harness. specifically one of the posts on the tail relay is what is shorting. blue wire with a white line and red hash marks on it. i can follow it to the firewall and into the back of the fuse panel but after that im lost as to where it goes. the only thing i havent pulled out of the car haness wise is this one because of how big a pain it is.
     
  10. Mech Addict

    Mech Addict Supporting Member

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    Funny how this discussion has gone as bits of the story are revealed. It made no sense to me that the frame itself was posing any resistance. Ohm's law (i=V/r) is a pretty accurate approximation, but there are some fine points to keep in mind. Often not relevant to wiring work, but it is really the voltage (potential) that compels a current to flow, with proportionality a linear function called "resistance". Actual voltage sources usually have their own internal limitations, that comprise an effective resistance (like a battery, a series of chemical half-reactions completed by electrons flowing through the conductors). But like many aspects of automotive repair, being well versed on practical applications will trump the theoretical fundamentals almost every time. In fact, often I am only more confused by having studied physics and thermodynamics, and my car remains in the garage.
     

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  11. wrencher

    wrencher Proven Member

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    I Have a fluke 78 and a fluke 88 and a 233.
    What model fluke are you using?
    Is it a calibrate-able version?
    How old are your leads?
    I have a EECT900 snappy power probe too.....
    ( ^ awesome tool BTW )
    Does it say the same in the DC setting?

    To have a bias voltage of .5 to 2.5 between chassis ground and battery ground?
    If it where so, the level of dysfunctional or non-functional circuits in your car would be numerous.
    Let alone tested with just a high impedance meter no electrical load present ?
    There are times when you have to think about the plausibility of what you test results are.
    I think this qualifies.
     
    a7xinsane likes this.
  12. luv2rallye

    luv2rallye DSM Wiseman

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    yep, yep, yep.
     

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  13. a7xinsane

    a7xinsane Proven Member

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    Yup I have the EECT900 and the fluke 88. They both read the same .50 on the strut tower nut. I walked away from it for a few hours today while testing it to work on a customers vehicle and went to return working on it and now i have good ground at MOST points on the chassis. the ground by the fuse box on the drivers side shows 0.1 off and on and the (maybe???) ground out of the flasher relay still shows between .4 with the lights on and .1 with EVERYTHING off... jiggling wires in the bay or inside the car doesnt seem to change anything... Im going to forget about the wierd voltage issue for now in hopes i will find my issue while focusing the turn signals but I am fearful the problem is one in the same. Since i walked back to it today whenever the 4 ways are on the stock boost guage and the dash warning lights( just coolant and battery) blink on and off with the relay. Boost guage swings up and down. Turn all lights off except 4 ways and no wierd dash light blinks. My cars got casper in the gas tank maaaaan. this shit is wierd. Usually see this stuff on landfill trucks and gas well bottles( my day job) but not clean wired cars...
     
  14. wrencher

    wrencher Proven Member

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    Chase your grounds back. DSM's are super easy.
    Battery to firewall
    Battery to starter bolt
    Intake to firewall ground strap.
    Drops should not exist with those clean present and accounted for.

    Here is all the locations of the grounds in a !GA referred to the OEM diagrams by their number.
    ( oddly a ground of interest for your cluster #9 )

    1G 1thru5ground.png 1gnumber1ground.png 1gnumber2ground.png 1gnumber3ground.png 1gnumber4ground.png 1gnumber5ground.png 1gnumber6ground.png 1gnumber7ground.png 1gnumber8ground.png 1gnumber9ground.png 1gnumber10ground.png 1gnumber11ground.png 1gnumber12ground.png 1gnumber13ground.png 1G6thru8grounds.png 1G9thru14grounds.png
     
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  15. a7xinsane

    a7xinsane Proven Member

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    Was missing #1 So i used 4 guage to make one. Changed nothing. all others are present and accounted for. took a surface conditioning disk to all the connection spots as well as dielectric greased the contact points and still having the same issues
     
  16. a7xinsane

    a7xinsane Proven Member

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    ok so I managed to find the problem with why the turn signals and brake lights werent working. Where the alt 80 amp fuse goes into the fuse block on the ground side of the fuse it goes to the alternator wires and a strip of metal running the length of the fuses. the metal strip had cracked and was almost completely busted off from the fuse box. I replaced it and EVERYTHING WORKS!!!! except the dash is still doing the funky blinking thing but at least I am making progress towards making it road ready... So back onto it to try and find out why the boost guage and dummy lights blink with the hazards and turn signals( way more dramatic blinking on the driver side turns/hazards) Thank you guys for everything. if it wasnt for the grounds location pics i would still be looking for all of them... As soon as I can figure out the dash lights thing then I will mark this post resolved...
     

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