Electrical Troubleshooting - Dead Battery

So it's a beautiful day in SC and the wife is out so I decide to take the trusty Diablo (99VT) out for a little fun.

 

However, for the 2nd time in two weeks when I wanted to do that, battery is dead despite being only a year old (Optima Red Top) and on a tender at all times. Last week it at least started with the help of my 200 amp jump cart. This time not.

 

So I take the massive rear wheel off to check the battery. Reading 9 volts out of the car, so I put it on the charger. I check all my connections with a meter to make sure the tender is actually able to do it's job - all good.

 

So then I check the battery terminals and across the + and - I'm reading 8 ohms of resistance with the key out and the battery totally disconnected. Not a dead short, but I believe a helluva lot lower than it should be.

 

So I'm thinking I have a short somewhere, although last week after jumping it the car ran fine and all systems I tried worked.

 

So normally my troubleshooting would start with just pulling fuses and links one by one until I see the short disappear and then start troubleshooting the attendant system.

 

Any better ideas out there?

 

Thanks,

 

- - charles

 

Did you check the alternator output once you got it started?

 

Hook your meter to the battery and check for drain on the system while everything is off. If you are showing a drain you can start by pulling fuses one at a time to see which circuit is causing an issue. Once you track down which circuit it is you can then go about figuring out why.

OK. Disconnected alternator - no change. Checked through fuses and discovered the draw is on Fuse 25, described as: "Courtesy Lights, Luggage Compartment Light, Stereo, Air Conditioning Memory - Brake Lights (+30ST)".

 

Now I need some help with how Lamborghini describes things. All through the fuse listings, certain functions include similar designations to the brake lights above (+30D, +30ST, +15P, +15D). What do those mean?

 

There is also a fuse (#11) marked "+15/30", described as: "Car Stereo - lights selector and +15/30 fuse". There is also a relay (#5) marked as "+15/30 relay".

 

Any idea what that fuse / relay / designation mean? I have the full service/electrical manuals to the car but they are still packed from our move. Thanks!

Well - I found the problem. Just not sure of the most permanent solution. Under each door are two spring switches. One appears to turn off the red courtesy light on the inside door panel. The other appears to be dome light control. The dome light control switch on the driver's door is not breaking the circuit when the door is closed, so it's leaving the interior dome light and the luggage compartment light on all the time.

 

The switch is good as it works properly when I press it in manually - just not when the door is closed. As a temporary solution, I folded over some cardboard from a pizza box and taped it into the door frame where the switches are supposed to make contact. Now it works properly, but my wife thinks it makes our Lambo look ghetto to have the pizza box taped to the door frame. I think it's an appropriately Italian solution, but I will defer to her.

 

So does anyone know if those switches are at all adjustable? They're covered in a rubber boot so it's not immediately obvious if the plunger reach can be adjusted.

 

I'd still like to know what all those designations mean if anyone knows. Thanks!

If you drain a Red Top completely, you will have to replace it I think. Draining them basically destroys them, and they will never perform like they should again.

 

I did it with mine, but got a new one on warranty.

It looks like Optimas require much higher charging current than a regular battery to come back. Check out their FAQ here:

 

http://www.optimabatteries.com/product_support/faqs.php#

 

Scroll down to where it says "How do I charge a deeply discharged battery?"

 

The fact that they want you to use a "helper" battery and they warn about temperatures indicates to me that they need a pretty high charge current - more than the 10 amps that an average car charger can do. They also indicate higher charging currents help break up the sulfation of an Optima battery.

 

My charger can do as much as 200 amps, so I think it will be fine, but we'll see... Thanks!

Sounds like maybe the length of your switch is too short, maybe broke some of it off? Pull switches from both sides and compare, then swap sides to see if it changes to the other door. If it does then just replace the switch.

 

As Placid said, unless you are using a yellow top Optima, once its completely cycled it should be replaced. You can attempt a recharge but most electircal techs will tell you the best that battery will ever be again is 60-70% tops. Problem you run into after that is now the alternator is working harder to charge and maintain your battery all the time, creating excessive work which eventually will lead to rebuilding sooner than expected.

 

When you consider the costs involved with parts and such for these cars, replacing a questionable battery after repairing the problem really shouldn't even be a question, why would you even chance it at less than $150? JMO $.02