Battery drain question
 

I have a problem with something draining/discharging the batter in my 77 911.

I've disconnected a cable from the battery post and hooked up a 12volt test light between the cable end and the battery.

I'm getting a dim pulsating light on my test light which pulsates on and off every second or two sort of like a turn signal bulb.

Could the problem be in the emergency flasher/turn signal relay or the e flasher or turn signal switch that causes this pulsating light and battery discharge or do I need to start looking else where? Thanx all L.

On my 76 911, there's a relay that flashes a light on the speedo when the handbrake is up. Kinda threw me off a bit because my 80 911 doesn't do that. I believe it's the same relay that supports the turn signals. However, that should only draw when the key is in the ignition and the ignition on. Maybe a short in the ignition?

I had a drain that killed the batter overnight. The way I found it was to connect an amp meter between the negative cable and the negative terminal of the battery. Once connected remove all the fuses, then insert each, one at a time. I used a fluke with the probes in the 10A ports. Don't forget about the three fuses in the engine compartment.

Tony

Tony yes I get this with the ignition switch off and key removed.

I'll check into getting an amp meter.

Do you have the stock VDO clock? It drains my battery.

When in doubt, unplug whatever you think may be the problem. Pull the relay, pull a fuse, unplug the clock, etc. Any change?

JR

Chasing electrical shorts can be a very frustrating process.
In my '74 I had similar issues. I found that the clock was part of it, as well as fried wiring resultant of a poor alarm / stereo install. My major culprit was a relay in the alarm system.
My suggestion is to download the current flow diagram from the Pelican tech area and if you can, print it out on a large scale printer. Then work your way through the likely circuits by, as suggested, pull the fuse and isolate the different halves (in front of and behind) the fuse block. Bear in mind that a current flow diagram is not exactly a wiring diagram - so you'll have to wrap your head around the logic of it. It's not a point to point map, but a diagram of how current flows through the various circuits and to ground.
Lastly I installed a battery disconnect that I'll dis-engage the battery with when the car is going to sit for more than a few days. That kills the clock, but that's not a big worry for me. Maybe one day I'll invent an isolated circuit with it's own NiCad battery for the clock.
Patience is the most important tool in this chase...
-C

Yes I still have the factory clock but it doesn't work.

I'll start with the fuses in the front trunk and go from there.

Doesn't work may not be the same as 'doesn't draw current'... just a thought.

Chuck.H
'89 TurboLookTarga, 365k miles

Here is another way of finding the problem. Disconnect the negative cable from the battery. Start with the fuseboard in the front trunk. Pull one fuse out at a time then lightly touch the negative cable connector to the negative post on the battery and look for a spark.

This way may not be as accurate as using an amp meter but if you have a big enough draw on the battery to discharge it over night or in a few days you'll see a spark on this circuit for sure.
Good luck with this.

Here is a video showing how to track a parasitic draw from the battery and measure how much. Watch to the end, to see the easiest way to do it with a volt meter.

3 Ways Of Finding The Cause Of Key-Off Battery Drain (Parasitic Draw) - YouTube

I think I've found the problem. With the test light wire connected to the negative cable from the battery and the probe of the test light touching the negative post of the battery the pulsating light goes out when I disconnect the ignition switch wiring loom.

I disconnected the short round male plug wiring harness that runs from the back of the switch to the round multi pin connector on the body of the car.

So would this be the electical part of the igintion switch that is bad? How difficult is it to remove from the metal body of the ignition housing.

More likely it is something downstream of the switch. I don't have a diagram in front of me but I'd suggest tracing all the circuits that it feeds.

JR

JR any idea where I can find the ignition switch wiring diagrams for my 77 911. I don't have the factory workshop manuals.

I've hooked up an amp meter and I'm getting 30 milliampres draw off the battery. Is this reading too high enough to drain the battery.

I think you want to find the fuse that's pulling m/amps, you then know which circuit to focus your attention on
Rewatch the video again and follow the steps in the last part. Shows how to check each fuse

I don't know where to find a diagram for a 77. You might try a Clymer manual.

30 mA isn't that bad.

JR