2008 v6 electrical short?

[07blowngt]

I have a 2008 v6 mustang. After the car sits a week or so the battery is dead. The battery is brand new. I unhook the negative terminal and put a multi meter between post and ground cable. is showing 13 volts. Pulled all fuses under hood, relays and also in the car by the passenger kick panel. voltage never changed. unhooked alt and starter, no change in voltage. Is there something else I am missing to check that could be pulling battery down?

 

[Juice]

First thing to do is measure current draw with everything OFF. Doors closed, wait till dome light goes off (or lock car with remote). Draw should be minimal.

Do you leave the key in the ignition while the car is parked?

Ps: Cars with body control computers (SJB) WILL draw the battery down over time, as the computers never really turn off all the way. For example, my 08 Clubwagon (sits a lot) will drain the battery in about ~2 months, so I keep a 1Amp automatic charger on it.

 

[redfirepearlgt]

Assuming 25mA (.025A for the novice) current drain on a 45aH battery (avg aH rating of an automotive battery) fully charged the drain time estimate would be 75 days(45aH/.025A=1800 hours or 75 days). Obviously the ability for the battery to generate CCA enough to turn over the will have been depleted well before that time. CCA btw is the full charged rating of a battery to produce that amount of amperage for 30 seconds at 0 degrees F before the voltage potential drops below 7vdc. Amp Hour rating is the length of time a battery can provide current at a given load before being depleted.

If OP you are experiencing a complete battery depletion to the point that the dome lights don't even turn on in a period of 10 days (240 hours), this would roughly equate to a current draw of approximately 5 amps. That significant and when re-attaching the battery would create a very nice arc at 12.5 vdc (62.5 watts of power). As mentioned above you need to be measuring for current draw in this case.

Verify the current measuring ability of your meter before jumping into this and that you know what you are doing. Current is measured in series not parallel. Most meters are rated at 10amp max. On rough estimation you are going to be seeing approximately half this current if not more. Again this is an educated calculated estimate and not stone fact. A current clamp (aka amprobe for the old timers) capable of measuring DC current (an AC current measuring clamp only will not work) will be needed for measurements higher than 10 amps and would be the more suitable and safer option for you but they aren't cheap.

You can arc weld with a car battery. Think about it. If that battery can produce 775CCA for 30 seconds that is peak wattage of 9678 watts. Touch a 60 watt incandescent light bulb that has been turned on for longer than 30 seconds and see how warm it is at 6% of the wattage this battery can produce peak for 30 seconds. Don't take DC circuits for granted.

Just be careful and get assistance from a friend if you are not familiar with doing current measurements. EGO's kill as many lives as anything. Be safe.

And of sermon.

 

[07blowngt]

When I measure across the ground on the battery terminal and the cable I am getting 6.11 amp draw. Where would one start to figure out what is drawing that much amperage?

 

[Juice]

Start pulling fuses/relays one at a time until you draw goes away.

Note: I would check the draw with the alternator's regulator wires unplugged. I've seen bad voltage regulators "stick" on and not turn off the field circuit. 6 amp draw is in the ballpark for the field circuit. According to the wiring diagrams, it is fuse F43, 10Amps.

 

[redfirepearlgt]

When I measure across the ground on the battery terminal and the cable I am getting 6.11 amp draw. Where would one start to figure out what is drawing that much amperage?

WOW! My calculation was only 1 amp off.

6 amps is huge. I agree with above. For fun first pull F43 (10 amp fuse) in the BEC box under the hood. It feeds voltage from the battery to what I believe is the regulator circuit inside the alternator. If the current draw goes away replace the alternator. If it does not next disconnect the cable on the back of the alternator marked B+. IT will be a significantly larger red wire. Be careful you don't arc this straight to ground as it is carrying full battery potential and it will get ugle VERY fast. Take you amp meter out of circuit, leave the battery pos disconnected and disconnect and ISOLATE the alternator connection and measure current again. If the current draw is gone ....guess what? Replace your alternator.

If this all checks correctly, place everything back together and begin as mentioned isolating systems one at a time by pulling the fuse, checking your current draw reading on the and putting the fuse back if nothing changes. Obviously, only pull one fuse at a time and put it back in so you don't accidentally put a smaller fuse into a larger service socket by mistake and compound problems. Once you find the system causing the problem we can begin dividing and conquering that circuit.