12.75v draw on battery-can not find problem

[MkDiego]

I have done the following while troubleshooting:

• Removed all fuses, relays, and diodes in both the fuse block next to the battery in the engine compartment and the fuse box at the left side of dash.
• Unpluged ALL wire connections at the following areas - under the hood on all engine components - behind the left and right front kick panels - under the complete dash system - ignition switch - under both center consoles - and the brain box (computer) under the dash at the forward center console - and also unpluged the altenator.
• I even removed the 60amp and 100amp fuses in the fuse box next to the battery.
• NOTE 1 : then and only then will the 12.75v stop - now when I reinstall the 100amp fuse the draw comes back.
• NOTE 2 : when I seperate the two wires at the positive battery post and only hook-up the main cable to the starter I do not get any voltage draw on the battery.
• NOTE 3 : If I install only the secondary positive cable that goes to the 100amp fuse, and not the main cable going to the starter, the voltage draw comes back.

[Cat Fuzz]

What do you mean by "voltage draw"? Where are you putting your meter probes? When talking draw, it refers to current, not voltage. Is your battery going dead while sitting?

[MkDiego]

When the battery is disconnected it will hold a charge with no problem.
I can put the meter between the negitive battery post and the engine and it will read 12.75v. I can switch and do the same thing but with the positive post and the engine.
If the battery is left connected and let set for 30 - 45 minutes the car will not start.
The meter in the dash shows that it is charging the system at around 13+v
When I have to jump start the car (if I don't disconnect the battery when I park it) it will start up right away and the alt. will charge up the battery with no problem.

[rodeo02]

Taking an inline voltage reading like that doesn't mean much. Measuing a current (amps) means something is pulling on the battery. This could be just a weak/bad battery or an alternator that is not maintaining a charge. If you are not seeing ~14VDC across the battery terminals on an idling truck, something is up with either the battery or alternator.

Joel

[MkDiego]

Originally Posted by rodeo02

Taking an inline voltage reading like that doesn't mean much. Measuing a current (amps) means something is pulling on the battery. This could be just a weak/bad battery or an alternator that is not maintaining a charge. If you are not seeing ~14VDC across the battery terminals on an idling truck, something is up with either the battery or alternator.

Joel

OK I started up the thing, and at idle with a meter across the terminals the reading was +14.67v.
While it was running I also pulled the positive cable off the battery and the thing kept running without a problem.

[Cat Fuzz]

Ok, if your reading voltage from battery negative to the engine thats not a draw, thats a voltage drop. You should be reading close to zero volts in that situation. You must be missing some ground straps from the engine to the frame. In other words, your engine is not grounded properly.

[Canucklehead]

Originally Posted by Cat Fuzz

Ok, if your reading voltage from battery negative to the engine thats not a draw, thats a voltage drop. You should be reading close to zero volts in that situation. You must be missing some ground straps from the engine to the frame. In other words, your engine is not grounded properly.

I have to disagree with your diagnosis here. A bad or missing ground is going to prevent a component from coming on, therefore it won't be a current draw. A battery that won't maintain a charge overnight has some load on it which would indicate a switch or relay or something sticking shut.

That being said, finding components that are drawing current and draining your battery is something that has to be done logically. You can't just pull all of the fuses and relays and then start looking. What you need to do is replace all of the fuses and relays you removed. Then, disconnect the negative battery cable. Use your multimeter as an ammeter (or test lamp) and jump the negative battery cable to the negative post on the battery. If you have current flow (or the test lamp is lit), something is drawing current. Now you want to pull fuses and relays one by one until the current is no longer flowing. This will at least keep you from easter-egging and banging your head any more.

[Cat Fuzz]

Originally Posted by Canucklehead

I have to disagree with your diagnosis here. A bad or missing ground is going to prevent a component from coming on, therefore it won't be a current draw. A battery that won't maintain a charge overnight has some load on it which would indicate a switch or relay or something sticking shut.

I didn't say his reading indicated a current draw. Measuring voltage from battery negative to a point that is supposed to be electrically the same point should give a reading near zero volts. The engine should be connected to battery negative (grounded) essentially being a piece of wire in a circuit. You shouldn't be able to read a voltage drop across a wire with no load. There are other issues here besides a draw on the battery.

Switch your meter to the amp setting and disconnect the negative battery cable. Remember to switch your positive lead to the amp jack on your meter and then, with everything off in the truck, place your meter INLINE between the negative terminal of the battery and the end of the battery cable. This is how you read current in a circuit. Mind you, if you think that the current draw is over 10 amps, don't try it. Most common meters won't read more than 10 amps. One way to test, before you fry your meter, is to place a 10 amp inline fuse between the neg terminal and the negative battery cable. If it blows, don't use your meter to measure the current draw. Or, if you happen to have an inductive amp clamp, you can do it without removing the battery cable and safely measure several hundred amps, depending on the amp clamp.

[Canucklehead]

Originally Posted by Cat Fuzz

I didn't say his reading indicated a current draw. Measuring voltage from battery negative to a point that is supposed to be electrically the same point should give a reading near zero volts. The engine should be connected to battery negative (grounded) essentially being a piece of wire in a circuit. You shouldn't be able to read a voltage drop across a wire with no load. There are other issues here besides a draw on the battery.

Switch your meter to the amp setting and disconnect the negative battery cable. Remember to switch your positive lead to the amp jack on your meter and then, with everything off in the truck, place your meter INLINE between the negative terminal of the battery and the end of the battery cable. This is how you read current in a circuit. Mind you, if you think that the current draw is over 10 amps, don't try it. Most common meters won't read more than 10 amps. Or, if you happen to have an inductive amp clamp, you can do it without removing the battery cable.

You know, after reading MKDiego's second post I am confusd by what he is actually doing. When I first read it I was under the impression that he was checking from Neg. termianl to ground with the negative battery disconnected - should get battery voltage. And then he reconnects the Neg. cable and disconnects the Pos. cable and gets battery voltage again, when checking from Pos. terminal to ground... should be 0V. This, to me, indicates something is "staying on".

After your post and going back and rereading MK's it now sounds like a bad ground, especially if the cables are connected when he's taking voltage readings. If that's the case, as you said there are other issues.

[MkDiego]

Well I fell like a fool today and just wondering why I bother to get out of bed in the morning...
Fixed the problem - Cost $42.00 for a new battery. Works good, last a long time.
Oh well I just call it "having a senior moment"... end of story.

I really do appreciate all of the inputs. Thanks again.

[Tom01Rodeo]

Originally Posted by MkDiego

Well I fell like a fool today and just wondering why I bother to get out of bed in the morning...
Fixed the problem - Cost $42.00 for a new battery. Works good, last a long time.
Oh well I just call it "having a senior moment"... end of story.

I really do appreciate all of the inputs. Thanks again.

Ok, good deal. But for future reference, do not disconnect the battery while the engine is running. It proves nothing and can damage electronics.