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Electrical Grounds

I have a 2000 Hyundai Elantra that I can only start by jumping the negative battery terminal to the frame.
Q1 - any guidance on how to find the faulty ground (I looked but its not obvious to me)
Q2 - would there be any harm if I made my own ground from the neg bat terminal to the frame?

No problem making your own ground. The bad connection is from engine block to body/frame. The ground was probably disconnected and never put back on. You can ground from metal on the engine to the frame where there is a handy bolt. The cable can be found at Wal-Mart or any parts store. It’s just a battery cable. Maybe somebody replaced your original cable with the wrong one.

Agree with @pleasedodgevan2. At the first sign of electrical problems…I add a ground strap from the engine to the frame and one from the engine to the vehicle body. It might be overkill but it’s cheap and sometimes effective as well.

Q1 - I believe you have a bad ground to the engine block. Check the negative cable between the battery and engine block.

Q2 - More grounds can never hurt. The most durable set-up for proper grounding I’ve seen and experienced is to run the high-amp cable from battery to block, and use an 8 ga or 10 ga wire from the battery terminal to a clean fame or body connection. The high amp wire to block needs to be there to have a good circuit connection for the starter, the highest amp draw of anything else on the car. The 8 ga handles the rest. Additional grounds btween frame and engine are also good.

It might also just BE the actual negative bat cable. I worked on a vehicle which wouldn’t start; otherwise was ‘ok’ (start by jumping etc.) - but the negative bat cable was BAD. Looked fine. Not a problem with it; except that it really wasn’t all that good. A new cable - fixed the problem. And more grounds never hurt a thing…

Your car should have at least two ground wires coming from the negative battery post. The large heavy gauge wire should tie to the engine close to the starter to handle the large amount of current needed by the starter motor. The other smaller ground wire which may be around a 12 gauge wire should tie to the chassis close to the battery. A lot of wire problems are caused by the battery acid getting into the wire connection at the battery and it corrodes the wire internally so the trouble isn’t noticed visually. If you do replace your chassis ground wire use at least a 12 or 10 gauge wire to replace it with and make sure it bonds to the chassis well. If you think you have a bad wire you can check the resistance of each end of the wire using a DVM meter to see if there is excessive resistance in the wire.

Everyone, thanks for all the advice and guidance. VERY much appreciated. In following up on resetting the ground, I discovered that the frame is occasionally now at 12v! I’m starting another thread titled “Body frame intermittently at 12 volts” with additional details.

No need for a new thread…The solution to your problem has been answered here…

I’m desperately trying to understand this, and would greatly appreciate pointers to any car electrical/wiring tutorials or books that would address issues like this; the only information that I have been able to find on-line is very basic info.

The original symptom was that when I tried to engage the starter, all electrical components shut down. Everything.

I have confirmed that the engine, frame and body are all connected, using the resistance setting of an analog multimeter (old school here in that mine is analog and not digital), showing near zero resistance. I also verified that the wire that connects the neg bat post to the body is good in that it has zero resistance. However, when I check the negative battery post against the frame or engine (when it is connected), there is a voltage potential from there to the post, except when I have a separate direct connection from the post to the engine/frame (accomplished with a jumper cable). How is that possible? I’m obviously missing something. By my thinking, if there is a potential when not connected, there would be current flowing when connected.

Oh, and when the system is in a “state-of-failure” and the negative battery cable is disconnected, there is ~ a 10 v potential from the frame to that negative battery post. However, when the system is re-set (i.e. I get dash board lights on) there is no potential from the frame to the battery post (as I would expect).

When you engage the starter, all electrical components shut down because they are supposed to. The ignition switch cuts out every circuit that goes through it except for the starter. A few things, like headlights get power because the ignition switch is not in their circuit.

To understand what is going on when you disconnect the negative battery terminal, you need to understand voltage dividers. I do not want to take up a whole lot of this websites capacity to explain that so I suggest hat you got to the website Volume 1, chapter 6 will explain, but you may need to read chapters 1, 2 and 5 to fully understand chapter 6 which is on Kirchhoff’s Law. Concentrate on series circuits and Kirchhoff’s Voltage Law.

Heres a link to get you started.

The short answer here is that it looks like you need a new negative battery cable. If the starter won’t work with the cable hooked up but does work when you add a jumper, then there is either an issue with the cable or the battery. If this is a factory cable with molded ends, the problem could be inside the terminal at the battery end where the cable does not make a good contact with the terminal, inside where you can’t see it.

When you put an ohmmeter on it, you are only passing a tiny amount of current, a few milliamps. Even a tiny contact area will give you a low resistance reading, but when you try to pass several hundred amps through that small connection, the resistance goes way up and the voltage drop across the connection also goes way up.

There is a small possibility that the issue is in the battery and the jumper cable has nothing to do with it. You first try to start, nothing happens, but inside the battery, there is activity that starts heating things up. By the time you connect the jumper cable, the battery has heated up enough to start working anyway and would have started the vehicle even if you didn’t hook up the jumper cable. Tiny possibility but still possible none the less.