NYCCDSM

TurboMike

Now that I got my DSM back and its all new goodies I seem lose a lot of battery juice after its been parked a few days.

Here's something I noticed: When I put the key in the three battery charge lights are very dim. Hmmmm.

This is how the stock setup works:
The three battery lights (battery, coolant, and something else cant remember) come on when you put the key in. They get 12v from the battery and then a ground from the alternator's ground. About a second after you start the car, they go out. Thats because as soon as the alternator starts spinning it puts its voltage on the other side of the bulb. The 12v from the battery and the 14v from the alt cancel out and the bulbs shut off. So when the alternator screws up and starts putting out like 7v or less, the bulbs slowly start glowing because they get more voltage from the battery than the alt and they start to light up.

So my bulbs are very dim when the motor is off (power from battery and ground from alt).

What the hell does that mean?

Short between the battery and the bulbs?

Short in the alternator so there is a weak ground to the bulbs?

They shut off fine when I start it and dont come on.

koolyboy · Posted: Sun Dec 19, 2004 1:42 am Post subject:

Check your current drain with the car off. Shouldn't be very high, maybe 100mA. Much higher than that and you have a drain somewhere. Otherwise it could just be the battery not holding the charge. See if you have enough water in there.

TurboMike · Posted: Sun Dec 19, 2004 1:18 pm Post subject:

Can you check draw with a multimeter? Disconnect battery and run meter in between? What do you set it to?

MikeL · Posted: Sun Dec 19, 2004 6:04 pm Post subject:

I would HATE to have to diagnose an electrical issue in your car Smile

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koolyboy · Posted: Sun Dec 19, 2004 9:08 pm Post subject:

Kokomo · Posted: Mon Dec 20, 2004 12:43 am Post subject:

The general guideline for parasitic draw when the car is off is ~50mA from most manufacturers. Cars like BMWs, MBs, and other electronics laden luxo cars have a tendency to die in the winter because of draws that are above 50.

It seems if the dash lights are a bit weak just running off battery, you would check the electrical path for the dash. There is a main fuse for that inside the car, sometimes a bit of extra internal resistance introduces itself into a fuse or connector so it consumes some of the voltage that is supposed to go to the dash lights. Checking at the fuse is one way to see where your voltage is being used. The wiring itself should take up that much voltage but if its excessive, you know that's where your problem lies.