Help from electrical guru's please

[JackS]

Due to extensive traveling with my job, there are times when I leave my 89 Carrera in the garage for 2-3 weeks without driving it. It seems that something is draining the battery during these long periods of inactivity. The battery is one year old, the alternator belt is tight, and it holds a charge just fine once I drive it for a while. If I drive it once a week I don't have this issue.
Any ideas what could be causing this? Could a bad ground strap cause the drain on the battery? Any suggestions would be appreciated.

[ruf-porsche]

Electronic equipment such as audio requires a small amount of electricity to maintain the memory preset. Could be something as simple as a light bulb in the trunk, glove box or engine compartment not going off.

[RoninLB]

Originally posted by JackS
Any suggestions would be appreciated.

probably routine elec drain. I'd measure the drain and wouldn't be concerned of a problem unless I saw over .060 amp. There are the routine battery on/off sw that can be used. I use the marine battery lug that has the wing nut to attach the cable. Or if there's an alarm consideration I'd probably start by measuring the alarm drain and then maybe a sw to shut down car drain and leave only the alarm drain connected. The problem with starting the car with a 1/2 beat battery is that your loading the alternator and regulator when you don't have to.

[Randy Webb]

How old is your battery? If tired then the clock drain, etc. will do it in over the 2 weeks, esp. in winter. You may just need a new battery.

[makaio]

My 86 is the same way. I have hunted down all the paths, with no results. I now just disconnect the ground from the battery when I leave parked for more than a week.

[scottb]

I bought a small Schumacher on-board charger. About $30 at my local auto parts store. When I know my car won't be used for a few weeks, I hook up the charger. It keeps the battery topped off, but will automatically shut down when it reaches the proper voltage. Works great, and no more dead batteries.

[Wil Ferch]

89 should be like my 85....standby drain (spec) is about 17 mA. Later cars like 964's have a standby drain of 64 mA or so.

In general ..look for uncommon problems when standvy exceeds 100 mA ( some references say much higher...like 400 mA..probably because later car's normal standby loss is even greater).

--Wil

[304065]

Jack,

Wil and Ron have given you the technical specifications. Now, how do you measure the amperage drain?

First, you need a good multimeter, Radio Shack has them for about $50. Or you could go nuts and buy a Fluke meter, the sky's the limit. Anyway, once you have something capable of determining amperage, you then:

1) Disconnect the battery positive lead.

2) Set the meter to DC amperage at the 10A scale

3) Connect the meter IN BETWEEN the battery and the positive lead, with one lead from the meter touching the positive terminal on the battery, and the other touching the positive lead. Be careful, the battery makes a pretty good arc welder next to your fuel tank.

4) Let the meter stabilize and then read the scale. On the 10A scale you shouldn't get any reading unless you left something on. Drop the scale down to read in milliamps, then reference the figures provided above. Now, suppose you have a drain of 400ma, that's a bunch. That kind of thing can be caused by current leakage from an oxidized window switch, for example.

5) Remove each fuse in the car until the current drops. So your clock is going to drain a small amount, you might pull that fuse first just to verify that you are reading stuff correctly. Eventually, you will pull a fuse that causes the reading to drop: that then tells you which circuit has the drain.

6) Using the electrical diagram, trace out every component that's on that circuit, and look for faults. You are looking for: oxidized, crusty connections, with green, white or brown junk on them; loose wires, loose nuts, loose connections; frayed or burned insulation; wires that are stretched around something or routed unnaturally; or the biggie, aftermarket CRAP like stereos and alarm systems installed by a prior owner using cheapo crimp connections, bright-colored wire, etc.

7) It's a pain in the butt but you will eventually find the fault. Good luck.

[JackS]

You guys are unbelievable! Where else on the planet can you get this kind of advice and information. John; Thank you for the detailed response and tutorial. I will print it out and keep it on hand! Fantastic! I'lll post the outcome. I did notice that the battery cables were not seated quite right, so I started by tightening them down. I'll pick up a muti-meter this week and do some more detective work. Thanks again. I really appreciate the help!

[yelcab1]

2 weeks worth is actually pretty normal. Disconnect the ground cable, or ... drive it more often.