Help finding a earth leakage

[rar110]

I have a pretty significant earth leakage somewhere. I get smallish sparks when I connect the -ve battery terminal to the body. Found by accident when spanner connected to seat base.

Last time I drove it some unknown wire coming from cabin side of the firewall to the engine bay driver side completely melted (smoke every where). Kept driving it after the smoke cleared.

It has something to do with it but no idea what. The wire just ends near the brake booster. I can’t see anything it was previously connected to.

Any suggestions on where to start.

I would send it to an auto lecy, but they all seem pretty hap hazard locally.

Thanks.

[Homestar]

If you have a small earth wire melting it sounds like you have a larger earth that has become disconnected so earth currents are travelling through paths they weren’t meant to.

Check all your earths - there will be quite a few, so go over the engine bay, around the headlights, underneath the vehicle, etc to see if any are hanging off.

The sparking when connecting to negative of the battery sounds like you have something drawing current all the time that shouldn’t be.

Start by removing all the fuses then try the earth terminal again - you shouldn’t see any sparks. if you have a multimeter, set it to the amps range - most go to a max of 10 amps - you’ll probably have to move the lead to another spot on the meter as well.

Put the leads across where each fuse is - with the ignition off I wouldn’t expect to find any of the fuses drawing any power - if you do find one, then you’ll need to investigate that circuit more closely.

[bee utey]

The sparks could just be the radio memory supply, checking actual drain like Homestar suggested is the way to be sure.

[rar110]

Thanks gents.

Another weird thing was voltage and amps reading with the multimeter.

I tried to measure volts across the same two points (-ve terminal and body) and got no reading. I checked for a reading across the terminals and got normal battery voltage.

I tried amps and got same, zero reading. I did get milliamps. I did move the plug.

How could there be sparks but no voltage?

[Homestar]

The vehicle is a negative earth, so measuring between the negative terminal and the body will give you a reading of zero.

[bee utey]

How could there be sparks but no voltage?

Radios contain a capacitor across the power supply to suppress electrical noise. This charges in an instant and won't read a significant current for more than a fraction of a second.

[drivesafe]

Hi and first off, it is commonplace to get sparks occurring as you connect the last lead to a battery, regardless of whether it is the positive ( + ) or negative ( - ) lead being connected last.

The last lead connected to a battery completes the circuit, and as bee Utey posted, some devices, not just the radio, will cause a short current burst, and this is where the sparks can occur.

What is not commonplace is where an earth lead heats up some much that it smokes.

This is an extremely dangerous thing to occur as there is no overload or short circuit protection in any vehicle earth/negative circuitry.

As homestar posted, you need to check all your earth/negative cables and securing points. And start with those connecting to your motor.

In the old days, it was actually a problem that if the earth on the block came loose or disconnect, you could end up with an earth return path through a gear box, and this could result in the tips of the gears being burnt.

[Dervish]

Sparking when reconnecting the battery is normal.

First step, find out what the melted cable was for - nobody has a hope of assisting you otherwise.

[rar110]

Thanks again. The problem is in the 1989 Perentie wagon. It’s about as basic a car of that era can get. But there’s still a lot of wiring.

The sparks occurred by accident when I was using a spanner tighten the -ve lead to the battery. The spanner end made contact with the seat frame. So one end of the spanner was on the -ve pole and the other end touches the seat frame. The spark was on the seat frame.

I might start by taking off the gauge panel and seeing were the fried wire went to. I can’t see where the engine bay side was supposed to end up.

[drivesafe]

Hi again rar110 and first off, there is no such thing as “-ve” in automotive electrical diagrams and while this type of symbol is used in ELECTRONICS diagrams, but it means there is a voltage below 0v.

In this case, as you are looking for a negative circuit problem, the use of “-ve” just makes it confusing.

Next, try measuring the voltage between the negative lead point you were tightening and the seat frame. The seat frame may very well be the problem, with something inadvertently making it live.

[rar110]

Thanks Tim. I’m only talking about -ve in the context of the negative battery terminal or pole. Shortening negative to -ve.

There is no volts or amps between -ve battery terminal and seat base.

[bee utey]

Thanks Tim. I’m only talking about -ve in the context of the negative battery terminal or pole. Shortening negative to -ve.

There is no volts or amps between -ve battery terminal and seat base.

The only way to measure current out of the battery is to disconnect the negative battery terminal and measure the amps, then milliamps if appropriate, by connecting the meter between the battery and the disconnected lead. The seat base should not come into the equation unless you're missing critical earth cables between the chassis, engine and body. Then you would need the volts setting and have loads switched on, e.g. the head lights and see where you have voltage drops.

[Homestar]

Don’t the Perenties have a known wiring fault where the main loom runs through the fire wall and rubs through? I think more than one has burnt to the ground due to this - I’d be checking that carefully.

[rar110]

Don’t the Perenties have a known wiring fault where the main loom runs through the fire wall and rubs through? I think more than one has burnt to the ground due to this - I’d be checking that carefully.

Thanks. When I rebuilt mine I routed the wiring on top of the chassis rail.

[rar110]

Apologies gents but idiot alert.
I had another look at the battery set up this morning. The earth lead was not connected to the battery but still tucked away in the back of the under seat box. I had only connected one end of the heavy cable that connects to the 2nd battery. So sparking is just normal when terminals are being connected.

I do have a slow current draw from somewhere which has flattened the battery, so will check across fuse terminals for voltage. And will try to find out what the fried wire was for and what caused the huge current draw through that wire.

[B.S.F.]

You probably know this, but just in case you don't.
To measure the current (amps) you have to open the circuit and bridge the open circuit with your meter; put the meter in series, it's not like measuring the voltage .
.W.

[scarry]

You probably know this, but just in case you don't.
To measure the current (amps) you have to open the circuit and bridge the open circuit with your meter; put the meter in series, it's not like measuring the voltage .
.W.


Unless using a clamp meter designed for DC,which i have.

This makes reading current draw so much easier.

[Blknight.aus]

FFR or GS?

you can get some funny results if the radio batteries and 24v alternator arent set up properly.