Earth cable from negative battery terminal

[UKPhilTR7]

For a year now, I have been having a battery drain. So I tried disconnecting the positive battery terminal, to try and stop this drain. However, after a week or so, the battery did not have enough juice to start the car. So a week ago I disconnected the negative battery terminal. I came to start her yesterday and there was enough juice to start the car.

I noticed that there is an earth cable coming from the negative battery terminal, which is connected to a turret bolt. Should this earth cable be here and would this be causing the battery drain? I know that the other end of the negative cable is connected to the block.

[Stag76]

If you disconnect either the positive or negative terminal, you have broken the circuit and the battery cannot
be drained by anything in the car.
The earth cable connected to the turret bolt is earthing the body and engine, and must be there. It will not be causing
the drain.
You can use a multi meter to determine if the battery is actually being drained, then disconnect things to see where the drain is.
Most likely source is the alternator leaking to ground via faulty diodes, but this usually drains a battery overnight.
It will be a very small current if it takes a week to flatten the battery.

[FI Spyder]

A battery can drain all by itself (usually towards the end of its lifespan). What happens is the lead plate(s) turn into lead sulphate (I believe that's the chemical if I remember right) and this flakes off and falls to the bottom of the battery. When this builds up to a high enough level (the deeper the wells at the bottom of the battery the longer it takes) it will short out that cell. Also the less lead now in the cell will also produce less electricity. This usually start with one cell (they don't all physically change at exactly the same time due to manufacturing differences) and after a few days the voltage on the battery will read between 10 and 11 volts. If the battery drains with either pos or neg terminal disconnected the drain is internal. Time for a new battery.

If the drain is only when the terminals are connected you may have an external vampire drain. With everything turned off put your voltmeter in 10A mode in series with one of the terminals to get a reading. It should be what is effectively zero (clock takes very little).

[UKPhilTR7]

Thanks for the reply. From what I am hearing there should be the two earth cables coming from the negative battery terminal. The big one to the block and the thinner one to the car turret. I will try connecting the multimeter to the terminals and see if there is reading. I have replaced the clock with an oil pressure gauge, so hopefully there will be no reading.

[kippy]

Phil,
I have a similar problem to yours with a power drain in my Stag as it happens but none the less a problem.
I have tried chasing down the issue with a multi-meter and , as I'm electrically challenged, I damaged the multi-meter and not in a good way. I know how to check for the power drain, as YouTube is a wonderful thing, but just take it methodically as just putting a multi meter across terminals in the incorrect manner will do the meter a mischief. Michael

[Stag76]

Hi Phil,
Have you measured current flow (amperage) before?
If not, you have to connect the multi-meter in series with the load (drain) in the circuit.
To do this, remove the positive battery lead, connect the multi-meter +ve lead to the
battery terminal, and the multi-meter -ve lead to the positive lead that you removed from the battery.
Don't let the battery +ve lead touch anything, and don't operate the starter, lights horn etc. while you
have the meter connected in series or you will create a load and blow the internal fuse in the meter.

If you get a reading, start disconnecting things until you find it, starting with the alternator.

[FI Spyder]

Many (most) multi meters have a separate outlet (marked 10A) where you unplug the positive terminal lead and plug it into there. This will give a safe hook up for up to 10 amps which will be safe with everything turned off when you hook up the meter in series. Don't forget to change terminal back to where it was after you are done.

I did have a vampire drain of 1/3 amp that would drain the battery in a couple of days on my Integra. After trying to trace it down for many months (I would disconnect the battery if the car would be left for more than a day) I discovered the cause. I had sprayed the ignition key lock with graphite (to minimise wear) which conducted current draining the battery with key removed. I sprayed it with silicone spray to flush out the graphite and problem went away and never came back.

[Tamas Petrunin]

Many (most) multi meters have a separate outlet (marked 10A) where you unplug the positive terminal lead and plug it into there. This will give a safe hook up for up to 10 amps which will be safe with everything turned off when you hook up the meter in series.

If you're going to do this I always try a lower rated fuse instead of the multimeter first just to make sure nothing is going to draw more than the multimeter is rated for (if your multimeter is 10A try a 5A fuse). If it blows the fuse then you probably just saved blowing up your meter. Some alarms/stereo/amps etc can have large initial surge current.

Most multimeters bypass their internal fuses on the maximum current setting so it pays to be careful.

If it shows anything more that 0.5A don't have the multimeter in circuit for very long, most are only rated for 10's of seconds every few minutes on the max current setting, also the test leads don't like it either (most are way too thin for any real current)

A good way of isolating this type of problem is by pulling fuses and watching the meter reading, when it goes to zero you know the fuse you've just pulled is the circuit that's drawing power, that'll help you to narrow down the fault, appolgies if I'm teaching granny to suck eggs.

[UKPhilTR7]

Thanks for the replies guys. Over the last few weeks, my attention had been taken off the car, with the birth of our third child. However, things are starting to settle down a bit now, so I can get a bit of time to go down to the garage and play with my tr. For some reason the wife was not too keen on me going to 'play' with the car. Over the next few weeks, I will try to track down the vampire drain on the battery with the use of a multimeter. I went and got myself a new multimeter (Click UT33B) which should help.

I do have a flashing led on the dash connected to the ignition, to come on when the car is turned off. That should only take a very small amount of power though and I would not of thought that it would drain it so fast. Over the next week or so, I will be able to give some updates as to how things are going.

[UKPhilTR7]

Last night I was able to get down to the garage and mess about with the multimeter. I put it in line as per “Stag76’s” direction to measure the current flow (amperage) before. With everything off, there was no reading at all, nothing (0.00). I know that it was working correctly as the flashing led on the dash came on. This led was not even making the meeter move at all. I then put the side lights on and the meter reading went to 3.15. I turned the lights off and the meeter went back to 0.00. All the time, I was being careful not to blow the meter internal fuse

I also connected the small black negative cable back to the turret and this did not take any drain at all, the meter stayed on 0.00. I think it is safe again to attach that earth cable.

From the evening’s findings, I now think that it is not a “vampire drain” any more, but a battery that is on its way out. The car has been standing for a week and when I measured across the terminals, it was reading 12.29. Not too bad. I will check this again after a full charge and there after day by day, to see the health of the battery.

Meter reading with no load:


Meter reading with side lights on:


Meter reading across the battery, after standing for a week:

[FI Spyder]

Doesn't look like a vampire drain but an internal issue. How old is the battery? There should be a sticker marking date of issue month/year usually by little round bits being taken out. Most batteries have a warranty of three years (pro rated). The last batteries I got from one on those dedicated battery places had a 6 year warranty. In the past two years I've had to replace my battery on TR7, Tercel and Integra. The batteries lasted from 8 to 10 years, the latter being an Optima red top but they have switch production to Mexico and now only last a few years so the battery place stopped carrying them because of warranty issues. With no load on the battery one cell (they don't die at the same time) may hold a charge (giving your 12.29V) but with a load on it (starting) it doesn't have any storage capacity so it drops out giving you 11 or less volts which makes starting marginal.

[Saxman]

This may sound strange but I had the same problem with my battery draining, thinking the battery was old and tired I replaced it and after a short while the same happened. It took me ages to find it and guess what it was? The plunger on the boot light switch was bent down and missing the plate, boot light always on! Arrrg!
Might be worth a check.

[Tamas Petrunin]

Just to double check there is no power drain try turning the meter to the lower current settings, you'll have to move the red lead back to the middle socket and try the 200 milliamp (200m) setting, if it still reads zero go down to the 200 microamp (200u) setting but if it's drawing anything within that range it really shouldn't be causing a problem, the natural self discharge of a battery just sat there with nothing connected would be similar to such a small load.

[UKPhilTR7]

Last night I went and checked the reading inline again, this time on 200m. There was nothing on the meeter, not even a flicker. Hopefully, the weekend I will get her running and then be able to check the battery across a few days to see the trend down. I have a alternator checker and last time I used that (a few months ago) it was reading all OK. All signs are pointing to the battery on its way out. All I need to do now is get a kit to put the battery in the boot and then I can get a bigger one. Will check the 200u setting tonight.

[FI Spyder]

Just to double check there is no power drain try turning the meter to the lower current settings, you'll have to move the red lead back to the middle socket and try the 200 milliamp (200m) setting, if it still reads zero go down to the 200 microamp (200u) setting but if it's drawing anything within that range it really shouldn't be causing a problem, the natural self discharge of a battery just sat there with nothing connected would be similar to such a small load.

With my meter on 10A setting one of my batteries years ago it read .3 amp which was enough to drain in a number of days. Not sure how low it will go or what the accuracy would be in that situation. If it's internal it won't read anything.