mmjb

ok so i got a brand spankin new battery, and put it in. Car turns over fine. Left it hook up to the terinmals over night and the next day i try to crank it and the batter is dead. For some reason something is draning my battery when the car is off. Anyone got any clue as to what it could be??

Turbonut

iTrader: (1)

Check glove box light. Check voltage when off about 11.5/12.5 volts. Start car 14/15 volts. Turn on all accesories and it shouldn't drop below 12.
Check for a drain:
Now turn off all accessories, turn off the car. Disconnect the negative terminal from the battery. Install your test light/MM between the negative post and the cable you just removed. If the light shines, then you have a current drain,make certain the key is off and the door is closed, and if you have a light in the engine compartment, unscrew it, this will cause a drain. Now if the light is on, go into the car and remove one fuse at a time until you see the light go off. At this point you have found the circuit that is draining the battery. If you go through all the circuits and none cut the current, could be a short between battery and fuse panel.

Icemark

Glove box lights are only on if the parking lights are on

actually the car should never be below 12 volts. With the engine running it should never drop under 13.5 volts, and typically be around 14.4 volts.

If you ever drop under 13.5 volts while the engine is running (at idle or otherwise) the alt or charging system is suspect and should be fixed.

EfiniGirl

I seem to have the same problem and I *think* it's my alternator. I haven't really researched a lot yet though...

robfeltner

I had something like that and changed the alt to a FD, everything is perfect now. Here's the thing with the alt, there's a diode that keeps your battery from discharging back through the alt, and if that is shot, then your battery can be drained while the car is sitting. An easy way to tell, it disconnect the cables off the post of the alt, wrap with something so they don't touch anything. Leave car overnight, try to start car next morning, if you find things are better, you know the alt needs attention. If you want an FD alt, contact silverrotor

Rob

mmjb

thats weird, so the alternator can drain the battery when its not running. argh, ill try the alternator trick and see if thats it.

Icemark

Only if it is wired wrong will it drain the battery

Icemark

No, it can not if the alt is wired correctly. Only if someone who dosn't understand how to wire in the FD alt (a FC non stock item) will have it drain the battery.

robfeltner

My alt is wired correctly, and the new FD works great! I'm not completely sure that the batt can be dranined by the alt, but it does seem to make sense if the diode is shot. Right?

mmjb

oh well, i guess ill have to get out the old voltameter and start looking for bad connections... anyways thx for the help guys.

Icemark

If you mix up the ignition sense and alt run leads it will drain tha battery. In addition on the FD alts they are wired to have a constant lead going to the alt instead of the ignition lead (as found on the FC).

So mix them up and you drain the battery. No diode, no relay needed. Just proper wiring.

robfeltner

Yeah Mark I know, but my 7 is a '91 and has the same wiring as the FD. So for me, all I had to do it get the huge alt in the car and plug it in. Right? His alt is the stock unit, and I don't think he wired anything incorrectly. Is it not possible that the stock alt can discharge a battery if the diode goes? Cause the alt is pretty much directly wired to the battery, you can read the car's volts from the alt positive post. So, what's to keep the alt from sucking a few amps when the car is off? Diode....am I right?

Icemark

Well the only way the diode can go is if again the alt was wired wrong.

But it wouldn't matter on a FD alt, because again it wires different than a S5 alt. It does not just plug in, it needs the sense line to 12volts constant, not switched ignition like on a S5, however there are many people that do wire a FD that way.