Battery Connection Help Options

[AvalonFal]

I've been having problems with the battery draining over a couple of days of non-use, so I'm intending to replace the PO's battery cables (a few splices in the current ones) and go from there. PO relocated battery to the rear trunk & that's OK. However, I came across this situation:

- Engine off, key out.
- (+) battery cable disconnected at battery
- (-) battery cable still connected

I measured across the disconnected (+) cable to the connected (-) cable & got a voltage of around .6 - .75 volts. Is this normal to have voltage across a disconnected (+) cable??

Car starts fine when battery is charged, but, as I said, battery loses juice after being idle for a couple of days.

[stugray]

Is there an aftermarket stereo in the car?

Or is the meter on AC Volts? (if on AC, then they can pickup that much noise).

Meter leads in the correct holes on the meter?


Edit: Another way you can see voltage on the car side with no battery hooked up: Galvanic reaction (you car is rusting right before your eyes)

[AvalonFal]

Yes, there is an aftermarket stereo in car. Meter on DC and hooked up correctly. Car has had most rust removed/neutralized.

I cleaned and tightened up a lot of the easily accessible electrical connections and now the voltage reading is down from .7V to about .25V.

Paul

[stugray]

You are probably seeing residual voltage for the capacitors in the stereo.

If you short out the + lead to the - for a minute, then check the voltage, it will likely be near zero.

[914Mels]

If your looking for a battery draw, you need to be looking at amps, not voltage. Hook up a amp gauge between the positive cable and the positive post and see what draw you have. Anything more than 40-50 milliamps is going to drain your battery. You don't need to buy a real expensive meter for this kind of testing, a ten dollar meter will work.

[Rand]

I would pull fuses and see when the parasite stops. That's an easy way to narrow it down to a circuit.

Heck you could even pull all the fuses as step one and see that the drain stopped. If you pull all and it still drains then somebody really hacked in that stereo and you can start with the hacker's work.

Add back just the essential fuses and see what happens.... You get the idea.

[AvalonFal]

After pulling fuses, relays, pins, cables and cutting spliced wires, I think I've narrowed down my current draw to 1 of the 2 larger (4mm2) unfused red wires that run from the battery up the tunnel - 1 to ignition switch & the other to the fuse panel. When I cut these 2 wires (they were already spliced because the battery was moved to the rear trunk & the wiring had to be made longer to reach it), all current draw stopped.

Now I just don't know which one of the 2 wires it is - ignition sw. or fuse panel.

Anyone know of an "easy" way to find out?? Also, where exactly does the 1 red wire end at the fuse panel? Thanks in advance.

Paul

[914Mels]

jump one of the wires and see if you regain your fuse panel power or ignition switch power

[stugray]

Put the meter in current mode (this usually requires moving the red lead to the other jack).
Set the selector to I-DC(Amps)

Connect the battery negative to car chassis.

Connect the red lead to the battery positive.
Connect the black lead to the red wire that you disconnected.
Read the current.

By putting the meter "in series" all of the current runs through the meter and it can measure it.

You can do this with each wire that used to be connected to the battery to find the "parasitic current draw".

If the circuit you are testing has a current draw more than an amp or two, you can easily blow the fuse in the meter, then it will never read current again (until you replace the fuse).
That is the #1 reason people have trouble getting the current measurement to work.
Either they blew the fuse when first connected, or someone blew it previously.
Cheap meters typically only measure up to 1 AMP.
Better meters can go to 10 AMPs, but even 10 amps is not much especially if you forget to put the leads back where they were and try to measure the voltage across the battery (instant fuse blown)

[mikesmith]

The wire going to the ignition switch is (almost) completely disconnected when the switch is off (power tap goes to light switch for parking lights).

Lots of stuff (including your stereo) will be getting power from the other wire.

Unswitched power is present on the hot side of fuses 10, 11, 12. A good start would be to pull each in turn to see what happens to your draw.

12 normally goes to headlight up/down relays. 10 is normally fog lights. 11 goes all over the place.

There is a spare battery power tap on the back of the 10/11/12 fuses that is a likely place for someone tidy wanting 'backup' power for an after-market stereo. I'd look there too.

[ClayPerrine]

Here is another way to measure amp draw on a car electrical system.

1. Buy 100 inches of 1 gauge bare copper wire, two big copper loop connectors, and two wires for your meter.

2. Cut the wires into 8 - 12 inch pieces.

3. Put the 8 copper wires into the loop connectors, and solder together. You will need to use a torch to get them hot enough to take the solder.

4. Remove the probe ends from the meter wires, and solder them on each end next to the loop connectors.


This makes a current shunt. If you did this right, you can set your meter to the millivolt scale, and place the shunt in series with the battery. Read the meter as if millivolts were amps, I.E. 10mv = 10A.


Oh..and always place the shunt in the negative battery cable circuit. That way if it hits ground, it won't throw sparks.

[Tom]

There is a very much easier way to make a shunt.
Use a 6" piece of #12 copper ground wire from a piece of old house wiring. Hook it to two thin bolts and connect a couple of 12" 12 gage wires to the bolts. Put alligator clips on the other ends. Now hook up a known current draw in series with the "shunt you just made. Hook the source to the battery in-line with the shunt. Measure the voltage drop across the shunt only at the two bolts. this is the voltage drop across that shunt for a known current draw. Now hook your shunt in-line with any other current draw and use a formula to figure out the current draw.
New voltage drop divided by the known voltage drop, times the known current draw, = the new current draw.
Tom

[AvalonFal]

Thanks everyone for the electrical info.

Getting closer, but I've hit a dead end. I've isolated the current draw to the larger red wire at the fuse panel that runs from the battery (+) post. When I pull this wire off the panel, the draw disappears. Of course, a lot of things also disappear, like interior and dash lights and many other accessories.

So, where do I go from here??? Is this wire 1 continuous feed from the battery to the fuse panel with no other connections in between? If so, do I need to run a whole new wire from the battery through the tunnel to the panel?

Paul

[stugray]

SO the draw is downstream of the the connection at the fuse panel.
Take each fuse out and see when the drain disappears.

If you take them all out and the drain persists, then the panel is the problem.