mg62

Sounds like good advice guys. Thanks.

82dukman

Ok, the battery cutoff switch goes between the battery post and the car terminal wire. I have side posts, so the battery cutoff switch screws into the battery and on the other side of a ****, the car cable connects to it. Takes about 5 minutes to hook it up.
Yes you are right about disconnecting a battery lead. Remove the black wire from the battery and it "opens" the circuit and thus no power flowing through the car. Of course you lose radio present in the meantime.
One other thing. When you hook up the battery cut off switch, all you have to do is trun the **** and it cuts off the power circuit, kind of like removing a battery cable.


[Modified by 82dukman, 9:37 PM 5/19/2002]

Rockn-Roll

It sounds like a drain. And, it could still be a blown diode in the alternator...it not only drains the battery, but also weakens the charging power from the alternator by introducing AC voltage...the incar ammeter will swing all the way to the right when you first start up the car cause the starter drains a great deal of energy out of the battery...it means the alternator is putting out high DC current. If you start the car up and the meter only swings a small amount, then I would suspect an alternator diode cause the alternator would be putting out high AC current as well as some DC, or the internal regulator could have gone bad.

It looks like a good one.

Yes, the red one will plug into one of the other three depending on what setting you place the dial on.

You will want to use the 20 setting in the DCV for a 12V system. It is safest to turn the dial before connecting the leads. The reason is that if you have the dial set to one of the DCA settings and connect the VOM to the battery to make a voltage test then you may fry the meter due to the high current (over 40amps) that will flow through the meter which was designed to see less than 10. If you aren't familiar with electrical circuits then it's safest to disconnect the VOM any time you want to turn the dial. Turning the dial won't always harm the VOM if it's connected...for example if you are staying within one of the color coded sections then you can safely keep the leads connected. In fact for systems where I'm not 100% sure of the voltage I would use the 200 setting, then if I get a reading below 20 then I would leave the VOM connected and turn the dial to 20.

Well, what I do is wedge the black lead under the battery post clamp so it stays there...then I just touch the red lead to where I want to check for voltage. It's a real nuisance holding both leads and trying to keep them steady on the terminals while reading the VOM and tracing circuit diagrams.

Yes, use the 2K setting first, then if the reading is less than 200 then switch the dial to the 200 OHM setting...if it's an overnight drain then the 200 setting would probably be more useful. You can take the leads off...like I said I wedge them under the post clamps, or sometimes use the clamps from jumper cables to hold them down (when the battery is dead the jumper cables are probably out anyway).

Hmmm, do you want the technobabble or straight english? I'll go with a mix I suppose then you can ask questions that pertain to one or the other. OHMs is a measure of the resistance in a circuit. Zero ohms means that there is no resistance, while infinite OHMs means nothing is connected...digital meters represent this with strange symbols like UHN for unknown, or OPEN to indicate it's an open circuit. It's part of an equation which tells us how much current and power a device is using...the most basic is called Ohms Law named for the guy who discovered it...it's: V=IR which means Voltage = Current * Resistance, or in the correct units: Volts = Amps * Ohms. The relationship is such that if the Ohms increase then the current decreases, or if the Ohms decrease then the current increases such that the supply voltage doesn't change much...the only reason the battery voltage goes down is due to the battery loosing it's charge...with regulated supply voltages the equation holds true. If the current gets too high due to a decrease in resistance from something like a short in the wiring, then the battery drains faster. Normally the resistance should be more than 1,000 Ohm and that resistance coming just from the clock...with alarm systems there could be something like 300 Ohm. If you have an Ohms reading lower than that from the battery cables with the key off and battery disconnected then you have a short. The first thing I do is disconnect the alternator and then test again...50% of the time it's an alternator diode that has short circuited. The other 50% are obscure things like water in the license plate lamp, or a frayed wire touching something it shouldn't.

Hehe...I forgot that most VOMs now are digital. What I meant was 500 Ohms is about mid scale on analog VOMs...and that should be fine and not cause a good battery to drain over night. The VOM will display a number...at the 2K setting it should display whole numbers, at the 200 OHM setting it will probably display the tenths and hundredths...possibly thousands too.

Just because the alternator is putting out some current doesn't mean it isn't draining it when the engine isn't running. The alternator DOES go bad after awhile and I always suspect something that I know at some time WILL happen, then if it checks out OK then I look for something strange like maybe a screw driver finding it's way down the engine compartment and rubbing against a wire that finally wore through and is shorting against the frame...it's easier to find the alternator.

Yes you have it right. This is a test only if the OHMs reading is greater than about 50 Ohms (by the equation 1.2 Ohms would cause 10A, but there's always a current surge so I'm just being cautious), otherwise there may be more than 10A (including any surge) and possibly harm the meter. This way you can determine if it's within specs of any devices still connected, i.e. clock (about .01A) or alarm system (.05A). Also, if the meter reads 0 (zero) amps then remove the red lead, switch the red lead on the meter to the mA/BATT socket (the one just to the left of the 10A socket) and turn the dial to 200mA (stands for milli amps = .001 amps) and touch the red lead back to the battery terminal so you get the decimal amount of current.

Hope this helps...tracing electrical shorts is my worst nightmare...the thing about water in the license plate lamp is true...spent about a week at almost two hours each day before I discovered that one...actually it was a cop writing a fix-it ticket for not having the license lamp lit that told me where the short was.

Rockn-Roll

Hehe...IM DAVES80 on that...his car died when he was taking me for a spin in his ride...there was no power at all. He said it was some connection in the engine compartment and he just plugged it in better...it was on the passenger side so he blamed me for it.

mg62

If anyone needs evidence about why this Forum is so cool, they just need to read Rockn-Roll's long post up above, answering all of my inane questions in incredible detail.

Thanks for the info, amigo. I'll try to absorb it in the a.m.

mg62

Current status: The outcome of the DCV test on the disconnected cables was zero. The meter just read zero, and didn't jump.

I then did the Ohm test and the result on the 200 Ohm setting was a bunch of jumping around (numbers all over the place) and then it settled down to 7 Ohms.

I guess that means there's a short, huh?

stickboy

I have gone thru this before it takes a lot of patience. Make sure your dome/hood lights are out too. If you have your DOM set to sounds an audible alert when shorted because you run out of hands and can get a good view of the read out, the hood light will make it sound. Don't ask how I know this :mad

The_Dude

My underhood lamp did this to me in my '79. It didn't shut off when I closed the hood and completely drained my battery.

mg62

Neither my underhood light nor my interior light is operational (been that way since I got the car).

Biker

When ya get the car started, make sure the charging system is working properly. I used to have the same problem with my '81--ie, dead battery at start-up. I installed an on/off battery switch and the problem was solved.

Rockn-Roll

Yep. And 7 Ohms is very low...your battery is being drained at about 2amps...not many devices on a car will consume 2 amps...except the alternator, coil, and starter...I'd disconnect those three and test again...if nothing changes then start unplugging fuses one at a time until you locate the circuit that is causing the drain. Then use a wiring diagram to trace the wires to where they end and inspect the location where they end at on the car until you find the short. Until you get this short located and fixed and you need to use the car then get a battery post lock out as described above...there's no way that you can drive around with a 2amp continuous drain and expect the car to start even after parking for just an hour. Also, it's dangerous cause a 2amp flow though some wires will cause the wire to overheat, melt the insulation, and on many occations start a fire...you don't want that to happen. It would be safest to check the three devices I listed, and if it's not them then pull the fuses until the meter goes well above 7 Ohms...like I mentioned 300 Ohms would be safe for even an 18 guage wire. Once you find the circuit and MUST use the car then keep the fuse out...don't allow current to flow through that circuit until you fix it...if it's the brake lights then you could run some new wire out to the lamps...and cut the current ones so they don't short circuit in that direction...same goes for any other device...if it's necessary for using the car before you can locate the short then run some new wire around the short (use an inline fuse instead of going through the fuse box) and cut the current wires at the device/lamp.

mg62

I didn't get a chance to do any more testing. I've dropped the car off to get the ZZ4 installed, so I'm going to let the mechanics who're doing the installation isolate that short.

Thanks again for all your help on this. Having bought the VOM and used it a bit, I've certainly learned something that'll probably come in handy later on! I'll let you know what the short-circuit was once the mechanics report back to me.

mg62

This is just an epilogue to this issue, which ended slightly weirdly.

As mentioned above, I took the car in to get the ZZ4 installed, with instructions to the mechanic to chase down the short and fix it first.

However, the short seems to have spontaneously fixed itself! He left the battery connected overnight after I dropped the car off, and there was no drain. Same thing the next day. So, he just went ahead with the installation.

I picked 'er up yesterday, and she started up this morning like a rocket. Dunno what happened with that short, but I hope I've seen the last of it.

Thanks again for all the input on the issue.