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Discussion Starter · #1 ·
I have a jeep that can kill an Optima in a weekend if it sits still. I have tried different batteries and they die just as quickly as the optima. I tried to see if there was a short. I removed the negative battery cables and hooked a digital multimeter inline with the cables and re-grounded the battery. The reading on the multimeter did not change. It reads anywhere from 1-2 milliamps when it is not in use and the reading did not change when it was hooked inline. I have tried this method on about three occasions and have yet to find a short. My multimeter has a 10 amp max. I was not sure if it would notify me if it had a short of more than 10 amps. There will be an audible tone if more than 10 amps are presented. I have not heard a tone as of yet.
I don't want to pay someone to find the short. If you have ever done that than you know why. I will buy a battery disconnect and use it before I pay someone to find a short.

Does anyone else have any ideas or suggestions. [email protected]

375 Posts
Finding a drain on a battery is difficult at best.

With the ignition switch OFF, Try putting the ammeter in series with the negative side of the battery and note the reading. Next start pulling fuses one by one untill you get a reading drop. This might get you in the neighborhood of the problem. For instance if the reading drops when you pull the horn fuse, check the wiring for the horn.

its not much but I hope it helps

Discussion Starter · #3 ·
Here's the skinny:

Parasitic Load

Precheck--make sure there are no accessories such as phones, stereos, alarms, etc. that are powered up while the vehicle sits. Double check all lights; most parasitic load problems are related to this; i.e. glove box light, with door not closing all the way. Or, a shorted ground actuated circuit (interior lights, for example). Since it kills the battery in a couple days, the draw would be at least a couple hundred milliamps.

First, the DVOM must be set to DCA with the leads in series with the negative cable and negative post. Amperage can only be measured accurately this way, and be sure the leads are in the correct holes, or you just let the smoke out of a fuse (hopefully) in the meter. Also, if its an auto-ranging meter, you can probably leave it on the 10A setting, and normally they will scale to .01 A (10mA).

Now, normal parasitic load for today's vehicles should be no greater than 45 mA, depending on the amount of accessories the vehicle is equipped with (some surpass that, and some provide an ignition off draw fuse for removal if the vehicle sits longer than 7 days---all newer Jeeps have one). Note that several circuits these days need to 'time-out', and are controlled by Body Control Modules. You can watch the milliamps 'step down' 2, 3, even 4 times until it settles on, let's say, 19 mA. But, you needn't worry, since a CJ-7 in 76 is not equipped with these gizmos--unless added by the owner

**side note--some guys at my shop prefer the 'quick method' of installing a 12V test light in series with the negative battery terminal and post; Hang that over the hood (on a fender cover), and proceed to pull fuses, one at a time, until the light goes out. This is the circuit with the problem, and can usually be tracked down relatively quickly**

This would probably work for you, but I prefer the more accurate method of the ammeter for 2 large reasons:
1. Not all parasitic loads (especially small ones) will light all 12V test light bulbs, and
2. The level of load will often indicate the type of load: for example, a 200 mA load would not indicate all interior lights are on (that would be somewhere in the neighborhood of 5A)

So, in effect, you can tailor your diagnostics to probable load types with this method. However, in your CJ the trouble should be pretty obvious. Double check the hook-ups on the battery and meter; I've tracked down all kinds of electrical problems, and have spent the first ten minutes staring at a meter that's hooked up incorrectly....ahem, and I do it for a living

Finally, read your meter (or look at the test light) and pull fuses, one at a time. Once you narrow down the affected circuit, hook the battery back up and check for proper operation (this is where the schematic comes in handy). Make sure the component(s) on the circuit operates as designed, including powering on AND off.

If those tests are inconclusive, or your parasitic load is normal, its entirely possible your battery has developed an internal short. Leave it unhooked and see if it discharges....Optima is only a term, not an indication of reliability and performance

Good Luck, and sorry for the verbosity---especially since the side note should diagnose your CJ pretty quickly. Besides, you can't imagine what I left OUT of this post...

6,870 Posts
What Fortchman said!
(Very well done Fortchman.)

Might want to have the alternator checked for AC leaking past the rectifier.
AC will kill a battery in the exact manner you describe in a hurry, and since you can't find a large drain, and you have smoked several batteries, this may be a possibility.

Just start the vehicle and check for AC voltage at the battery terminals.
None is acceptable. Even if you get 5 or 6 volts AC at the battery, you have a problem.

I've seen the internal insulation in the Diodes give up the ghost for a variety of reasons, but I see a lot of AC leakage around the rectifier if the alternator has a lot of crud built up inside it, especially if you do a lot of mud and water fording.
Sometimes a disassembly and thorough cleaning of components (especially rectifier and AC insulation posts) is all that's needed, and some times it's just plain a bad rectifier...

Add a 10 Ga. ground wire from the alternator case to the battery while you are in there! You alternator will thank you for it!

Discussion Starter · #5 ·
Dear Forchman... you need coffee, two large bars of chocolate, a dozen beers, approx 100kg's of free weights, a large bottle of lucozade, and a night out on the twon in which your objective is to get laid. But THANKS !

Man thats some diagnosis routine... and to cut a long story short it must be parasitic load... as nothing else figures... my auto electrical know how goes as far as ... when you touch the permanent live to the underside of the car stereo it makes nice sparks... whoops.

Anyway... the last item on LEVE's post...number 4... whats that sposed to be hooked to ? I don't think i have one o them !


Discussion Starter · #6 ·
Had the same problem on my 81 cj ,it was a bad voltage regulator on altern.
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