Electrical Troubleshooting - 99VT Diablo - Dead Battery

So it's a beautiful day in SC and the wife is out so I decide to take the trusty Diablo 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

 

If the battery has a short, time for a new battery, right?

It has been a number of years but I swore off red tops because in my experience they are not that good at all, had all sorts of trouble with them, for instance, refusing to take a charge on a relatively new battery.

I only use Interstate now and it has been a really solid choice for my Diablos. Note I do have to "slice" off some of the plastic foot for the retainer clip(/clamp/formed piece of metal) to properly hold the battery down.

Now, if you believe you have a short, that's something relatively easy to test. Go down to Sears and pick up a 12volt continuity tester (about $5 -make sure it has a least a 10foot cable). Now, with your battery installed in the car, hook up the positive connection and leave the ground wire off. Hook up the tester to the negative battery terminal and with everything off including the 'gizmo' behind the driver's seat touch the probe to the shifter "pole" (which is a ground). If the test light comes on, bam you have a draw, then it is a matter of finding the draw. Note the light may 'flash' when you first touch to to the ground but if it does not stay on there is no draw.

If there is a draw, I would start by disconnecting the alternator as its dioide may be going bad and it can easily drawn down a battery in minutes if "fully reversed". The connector terminal for the alternator is on the driver side pretty much as you lean over the car looking down into the engine compartment you will see two big nuts (you may have used this as a connection for jumping or charging), unscrew the lead to the alternator (the one towards the rear). Retest, if there is still a draw then pull stuff, fuses, relays, etc, maybe first try disconnecting the entire fuse/relay panel and see if the draw is still there - before pulling individual items...

-J

 

why not just maintain it with a battery tender?

 

-mick

 

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!

 

Check that the door switches are turning off the lights when they're closed. It's not uncommon for the light to stay on (can't really see it with the door closed) and kill the battery.

 

Of all the forums, Tim wins the prize!! I was just about to post this but Tim beat me to it:

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!

 

The switches have a metal shim under them, between the rubber and the door. Some cars ive seen have one, others have two. You need a shim, either that or check the black plastic that is glued to the door post where the door rod attaches to is still there, if that fell off, this is the problem.