Alarm sounding off in the morning in 1989 3.2L

[Porsche 911]

Hello all,

Original alarm system here with the a single key hole to control lock and alarm system. The symptoms:

For about a week now, after I unlock the driver's side door to get to work in the morning, the alarm inexplicably sounds off when I open the door. I then need to close door and insert key again in order to disable the alarm. Weird thing is when I unlock door from passenger's side, alarm does not down off - normal operation.

The dashboard battery light has been flickering on occasion (2-3 times a week) for a couple of weeks now.

When I step on throttle while in neutral, I do notice a slight brightening of headlights a second or two later; dims back down when I let off the throttle.

Not sure whether the alternator needs to be replaced, the battery, or possible water seepage through the driver's side window seal is some how causing a short to the alarm system.

Any ideas? TIA

[darrin]

start by using a voltmeter to confirm that your voltage is spiking when driving -- the brightening of headlights suggest that your voltage regulator has failed and that your alternator is sending voltage spikes through your electrical system.

I'd recommend not driving the car for non-essential/non-diagnostic purposes until you confirm whether the voltmeter is spiking, as significant voltage spikes can damage electronic components (and cause your battery to bubble over, which I'd also check for asap) -- do you smell a sulpher smell (especially in the frunk)? -- that's a telltale sign of overcharging.

Once you've diagnosed (and potentially corrected) any voltage spike issue (voltage spikes can be fixed by having your alternator and voltage regulator rebuilt by an alternator specialist), you should have your battery diagnosed by a FLAPS (friendly local auto parts store) to see if it's holding charge, etc. Your alarm issue could potentially be the result of fried alarm electronics caused by the voltage spikes or a symptom of a dead/dying battery also potentially caused by voltage spikes.

[Porsche 911]

Thanks, darrin. Voltage levels (per FLAPS):

13.63 at 2000 rpm
13.43 after shutting it off

The clamp was difficult to get on the red terminal, though, so he had to hold it down while taking reading.

[darrin]

Voltage spikes can be very transient but are suggested by your brightening headlights observation (I also saw my dashboard lights do the same thing when a voltage spike occurred -- you might notice them as dimming from time to time)

Can you get a cigarette lighter mounted volt meter (there are some referenced in the "danger get voltmeter now" thread)? If you can, drive it with the voltmeter plugged into your cigarette lighter and monitor for spikes -- you'll see 16+ volt spikes if your volt meter/alternator is failing/bad

Since it sounds like your battery has proper voltage (i.e. isn't dying and giving your alarm too little voltage at rest), my concern is that the spikes could have fried something in your alarm, causing it to act funny -- when my voltage regulator/alternator failed many years ago (and before I understood what was going on), voltage spikes fried my tach before they were diagnosed and overcharged my battery causing some boiled over acid to rot part of the battery tray -- do you have records showing whether your alternator has previously been replaced? How many miles are on it?