A short in my fuse box

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21

OK, If I understand the problem, your battery is running down and when you disconnect the fuse box, thereby disonnecting ALL the fuses, the battery doesn’t run down. If I’ve got that correct, then one of the many circuits fed by the fuses is likely drawing more current than it should, or is staying on when it shouldn’t. Again, I’m assuming that the vehicle is running fine, and the battery runs down when the engine is off and parked.

The trick to effective trouble-shooting is to: (1)-assume that only ONE thing is wrong, and (2)-start with the EASIEST things first.

A very first check would be to measure the DC voltage across the battery. With a fully charged battery, and with the engine running it should be between 13.8 and 14.7 volts DC. Then shut off the engine and measure the battery voltage again. Without the engine running, it should be around 12.7 volts. If these voltages are OK, you can proceed under the assumption that the charging system and the battery itself are OK.

The next easiest thing to check in your case is to shut off the vehicle and remove the key; then inspect and check to make sure that everything that should be off to make sure that it IS off. Dome light, glove box light, fan, trunk light, under the hood light, cigarette lighter, rear windo defroster, radio, etc.; you get the idea.

If can’t find anything that way, the next easiest thing is to do is to connect a DIGITAL voltmeter across the battery on a low-voltage scale, (above 12 volts) and carefully note the battery voltage. Then remove each fuse, one at a time, and note if there is ANY increase in voltage, even a tiny one. That would mean that something connected to that fuse is drawing current from the battery. From the fuse assignments determine what it is and check to see what is on.

Alternatively, you could connect your DIGITAL meter in series with the battery feed, set to a HIGH ampere setting. Once connected propery, with the proper polarities, reduce the ampere range from highest to lowest until you get a reading on the meter. Again, remove each fuse until the current reading on the meter DROPS, even a tiny bit, and you likely have found a circuit that is continuing to draw current.

Try those things, and if no joy, come back with the results of the tests.

A Haynes manual for your truck will be very helpful in tracing the electrical connections. I recommend you get one if the suggestions above don’t locate the problem.

By the way, you must use a high-impedance meter. One of the newer DIGITAL meters should be adequate. Also, make sure your meter is set to the proper scale and range when using itand pay attention to the polarity connections.

Good luck.

22

Volts - Amps - AC - DC

You should be be able to get 35 V DC with the engine off. With the engine on refer to Tester’s response.

If you are reading 35 V AC and you are using a digital meter, it is possible you are picking up what I would call ghost voltage. Those digital meters are so sensitive they can measure voltages that are coming from outside where the wires are picking up radiated power like a radio does. These voltages are meaningless in this situation. If you were to read amps it would read something like 0.00000000000001 amps. That would not drain your battery even if was on.

Measure the amps (not volts) You may need a different meter or just connect a 12 Volt lamp in series with the battery cable and then start pulling fuses one at a time to find the one(s) that has a large effect on the reading. Get the manual and find out what that line feeds.

Or do you have a security system (especially an after market one) or an after market radio? They should be your first suspects right after checking for any lights left on.

Note: some cars will draw a fair amount of current for a while after they are shut off. Allow a hour or so before testing. Also by now your battery may have been damaged due to being run down and it may not be able to function normally.

23

Your testing method is incorrect. By placing the meter leads in series with the battery lead you are really trying to measure current but are you setting the meter to measure voltage. You need to setup the meter to measure current. This allows the current the system is using to flow through the meter circuit so it can be measured. I won’t bother with the details of measuring voltage or current except that when measuring voltage, the meter probes are placed in parallel with the load, and when measuring current, the meter probes are placed in series with the load.

As others have stated, there may be a problem with the alternator. There can be AC voltage present across the battery when the alternator is running if there are some shorted diodes in it. If you measure more than .1 volt of AC across the battery with the engine running around 2,500 RPM then the alternator is bad. The only place that AC voltage can come from is the alternator. Placing AC voltage on a battery will kill it pretty quickly.

24

First of all, I don’t think you know how to use a meter. There’s no way that it is remotely possible for there to be 35 volts ac on the fusebox of a car with a 12 volt battery in it.

I think you are going to have to find a mechanic that does know how to use a meter and can find your problem for you.

There’s probably not much going through a fusebox that could draw the required number of amps to kill a battery in 2 hours without being noticably on.

Things that could draw that many amps are:
Various fans,
Headlights,
Some sort of something plugged into a cigarette lighter outlet (Check those to see if a penny or dime has fallen into one creating a short circuit)

You’d obviously notice headlights burning, fans running. Dome lights can kill a battery, but it takes longer than 2 hours normally.

An open diode in the alternator could be the culprit. In which case you would need to have the alternator rebuilt (approximately $50 with a diode ring) or replaced (approximately $200 at XYZ Parts Store).

Skip

25

??Why are you using the AC voltage setting on a DC system and especially in series? The AC reading will always be screwy on DC voltages and mixed AC+DC voltages. Check with the instruction pamphlet that came with the meter. The meter should be set on DC amps in series then you can read the current draw in series with the circuit under test. Be cautious because if the current through the series is higher than the meter setting you can burn out the ammeter shunt resistors – new meter time if there is no fuse to blow. Don’t make the mistake of leaving the setting on DC amps and placing the leads between battery positive and ground – again new meter time.

One of the best ways to find battery current draw is to put a 12 volt test probe in series with the battery positive i.e. one clip lead on the batter positive terminal and the other on the positive cable clamp. If you get a light, pull fuses until the light goes out, then disconnect each unit serviced by that fuse until the the light will stay out when the fuse is inserted. That unit or circuit is the fault.

Hope that helps.

26

OK, let’s ask a few questions. This 25V AC you are seeing, is that with the motor running or not? If not, then I’d discount that reading altogether and switch to DC current on your meter. Then see how much current draw you get with the same hook up. It would be better to hook the meter up between the negative battery terminal and the negative cable. This will measure total current with the motor off and you can unhook one fuse at a time until you find the one that makes the current draw go down.

If that 25V AC is with the motor running, then I think you’ve got a bad alternator.

27

i am checkin with the motor off