May 15, 2011 - Battery drain

75557.2701@compuserve.com

I'm no expert on auto electical either, but I don't think you'll get anywhere measuring voltage. You have to measure amps... actually milliamps. I've done it a couple of times, but not on an Avanti.

First, check the car thoroughly at night, looking for any courtesy lights that might be on, especially under-hood, glovebox, trunk.

If you don't have a multimeter, you can buy one quite
reasonably. I have a large old analog Radio Shack model.

Start with a fully-charged battery, under-hood courtesy lamps disconnected or bulbs removed, and car doors closed or switches taped down, same for glovebox, trunk, etc... no courtesy lights on.

With the multimeter connected by test wires clamped between the
(disconnected) negative battery cable and the negative
battery post, you can measure the milliamp draw; but you need to start on a high amp scale on a multimeter and change scales until you get a decent reading, in order to avoid blowing a fuse on the multimeter (or destroying the multimeter). If the measurement is under 100 milliamps, suspect a bad battery might be causing the battery to lose charge over time. If above that 100 milliamp range, you'll need to check further.

Next, move on to testing the fused circuits (you'll need a list
of what's on the various fuses in the fuse boxes, which you
can find in the shop or user manual).

There's no simple method, you just have to begin removing
and replacing fuses until (hopefully) the milliamp reading
drops abruptly. You need to ensure all interior and
courtesy lights are out (including the under-hood lights)
when you take your readings. I generally leave the fuses removed until I complete the tests, but you can do them one at a time. Hopefully that testing will narrow it down to a fused circuit; then you need to disconnect devices from that circuit one at a time to determine which device causes the drain. If you never do get a drop, that means the drain is likely on an un-fused circuit, such as an alternator diode, the clock, parking lights, etc; so then you need to disconnect devices on the un-fused circuits to look for the culprit.

Go to youtube.com and search on ''battery drain'' to find
how-to videos on the process.



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Same thread

 2jimstadt@comcast.net

Stan,

Measuring 13.1 volts across an open switch is correct. Measuring 0 volts 
across a fuse or circuit breaker is also correct. If the fuse was blown 
then you would measure the same voltage as across an open switch. It 
appears you made the measurement on the open shutoff switch with engine 
running. A fully charged battery will measure 12.6 volts and when the 
engine is running the Alternator should output between 13 to 14 volts.

I read Wayne's response to your question and I agree that you should use 
an ammeter to diagnose this problem. The one procedure I do differently 
than Wayne is that I remove the fuses and then measure the amperage at 
the fuse box. Place the meter leads across the connectors for the fuse 
you removed and you can see if there is any current for that particular 
circuit.

As Wayne mentioned, there are a number of components that operate with 
the ignition switch off. The horns, brakes, interior lights, and clock. 
Check those first as the discharge is occurring with the ignition switch 
off.

Good Luck,

Jim