VehiGAZ

Do you have one of these buggers installed on your battery? (sorry for the crappy cell-phone pics, but it is identifiable anyway). Take it out before it leaves you stuck!

My PO put this one in earlier this year along with a new Interstate battery and it almost killed the battery. This disconnect functions by making a connection between the battery and ground when you tighten the green screw wheel, causing the metal on the underside of the wheel to contact the metal on top of the connector. When you loosen the screw wheel, it lifts off the top of the connector and disconnects the battery. Simple enough.

As you can (sort of) see in the second picture, the area where it makes this critical contact is very small, which makes it susceptible to heating (due to high resistance) enough to scorch the contact area, further decreasing the quality of the contact and increasing resistance. It was enough of a contact to start the car, but it was not a good enough contact to recharge the battery adequately, so about 5 months after installation, the battery died.

The car was in the garage nose-first, so I was trying to jump it at the battery, first with a battery pack and then from another car, and had a LOT of trouble doing that! If I had connected to the other side of the quick-disconnect, it probably would have started up perfectly. Anyway, after finally getting it started I drove to a local shop and had them check it out.

The battery recharged fine out of the car (and held the charge), there was no unusual drain on the battery when it was off (only 19 mAmp), and the alternator was outputting the right voltage to the battery. It was only when the mechanic compared voltage at the alternator and at the battery that he noticed something odd. A quick ammeter check revealed that the alternator's juice was not getting to the battery, and the quick-disconnect was identified as the culprit. I had him remove the quick-disconnect and got a tiny $80 bill for the battery charging and diagnoses. Not so bad!

One other seemingly-unrelated symptom was cured by this... the dash computer is supposed to hold the last function you had in the center display (such as outside temp) when you restart the car, but it never did - it always defaulted to instantaneous gas mileage [the LAST thing I want to know about this beast!]). I assumed it was because the computer was just old, but the removal of the disconnect and recharging the battery fixed that flaw as well! What was probably happening was when I started the car, the voltage dropped low enough and long enough for the computer to forget the last setting and default to the instantaneous mileage setting.

Big symptoms from a little cause. It's fixed now, though! And the shark is running again!!

Fabio421

This is the one you want. You should always install your disconnect on the ground side.

Kore928

I've been wanting to get a good disconnect. Can anyone recommend a good brand?

Alan

Blue Sea Systems (marine types) are positively the best IMO - but most of their units are quite large.

These types are quite suitable too (and cheaper) - this is what I have for my main battery disconnect - but you have to do some fabrication to attach any of them them securely & adequately electrically (these see huge currents). You can find these widely @ automotive stores.

Install at the rear ground point where the battery strap attaches.

I do have a Blue Seas Systems 3 way HD switch for my Aux battery set up - it is quite amazing quality equipment.

Alan

VehiGAZ

Ooh... I just realized that I have a great place to install a big honkin' switch - right in the amp board that now sits in my spare tire well! I can connect from battery to switch & switch to ground strap all under the board!

hacker-pschorr

I've had one of those on my 928 and my Audi for over three years now. I do take it off to inspect / clean it whenver I think of it.

Ron_H

I also have one of the less expensive disconnects on my car and have had it on for around two years. My gremlin will kill my battery in around 18 hours. We have searched and searched, but he hides when we're looking. So I gave in and just disconnect when the car is put away for the night. Lately, I have made the mistake of leaving it connected for around 24 hours and the gremlin has disappeared. I guess he just got tired of being lonely because I just stopped searching for him. **** on him. Good riddance. But now I have a bad starter connection. (maybe the gremlin went there.....? I'll flush him out tomorrow).

docmirror

Please note that in any of the 928s with a LH type FI brain, the disconnect will decrease your fuel economy significantly, and also make your car run richer, causing potential problems with the cats. The later the car, the more problems it will cause.

worf928

Please 'splain doc.

Do you refer to the loss of LH parameters every time the disconnect is used? Or something else?

Alan

I would not suggest turning your car off nightly (though I understand why some do). For me its emergency and convenience on the rare occasions I need to for some reason.

I have never felt the car performed in any way differently after a disconnection though - runs fins - idles the same, performs the same... maybe I am just lucky?

In any case one of the changes I plan to make when I install my auxilliary battery system is to power the alarm, LH and clock from the auxilliary battery.

Doc I was listening the last time you said this...honest!

Alan

docmirror

Yes, that is all. If one were ambitious, they could run a hot line as Alan suggests to the LH hot lead. although I can't find the keep-alive feed for the LH. I think the easy way would be to just use a DVM on the LH connector and go down the line with the key off until one found 12V.

Although I've heard opinions that the characterization doesn't take long, I assure you the cats must be fully hot, and the O2 sensor system must be operating in closed loop for the characterization to be complete. I'm sure it's a successive approximation algorithm, but everything needs to be up to temps for it to finish.

SwayBar

It must be a fairly large current draw to drain the battery in 18 hours!

Have you tried hooking up a multimeter in series with the battery to measure current draw with the car shut down (..make sure the doors are closed because of the lights)?

Once done, you can then start removing fuses and relays one-by-one, and each time checking whether the current draw has dropped. When the current draw drops, check which system corresponds to the fuse/relay which was just pulled, and then concentrate your efforts on that area while consulting the wiring diagrams.

VehiGAZ

I thought that to measure current draw properly with a multimeter, you need an ammeter attachment, which most people don't have. It's a loop that you hook around the wire under test (it opens and closes), and it measures how much current is flowing. Hooking the leads of a multimeter in series with the battery changes the resistance of the circuit, thereby changing the current running through it (V=IR, IIRC).

hacker-pschorr

I don't see how the temp of the cats would have anything to do with the LH computer. These cars do not have a second O2 sensor after the cat so the temp of the cat will have zero effect on the O2 sensor's reading. Otherwise cars with the X-pipe would have all kinds of issues.

I'm not saying either way about disconnecting the battery, just confused on the CAT theory.

F4GIB

I had the same experience on my older Taurus.

GET RID OF IT.