millermotor

I have a 1989 911 with 128k miles. I've owned it for 6-7 years and has always had a battery drain. I've always kept a battery tender on it during winter but would like to get the problem fixed this year. I've checked to make sure all cables are tight and secure. The one thing that has always been consistent is that the car eats through passenger side window switches. Other than that I have never had issues with the car until last fall. My wife and I took the 911 on a weekend trip 5 hours away(one way) to the beautiful side of our state. We put close to 800 miles on total. But as when we left home to the time we got close to our destination we never once stopped. About 1.5 hours into the trip the radio (aftermarket) stopped working, it would cut in and out. Didn't bother us, we just rolled the windows down and cruised. 4 hrs later we stopped for the first time for a beer break, came back out to the car to leave and the battery was completely dead. Wouldn't even crank over. The gauges all read great the entire trip, with no signs of overheating. This trip was also at the end of September in South Dakota when it was 55-60* out. We pushed it to a hill and dumped the clutch and she fired right up and worked fine. I drove to the nearest Interstate Battery center(10 miles away), shut the car off and went inside to see if they could check the battery. Came back out and it fired right up. The guys tested the battery and said that the battery was running a little low on voltage but still was perfectly fine. I was baffled. I drove to Oriellys to grab a cheap voltmeter and and then we went to our Air BnB for the night. Once we got there the battery showed 11.7-12volts. Went on with our weekend like everything was normal. There was a few times that it would barely fire up when we stopped but never left us completely stranded. When we drove home, we never stopped. But when we got home and shut the car off, it did not fire back up and only showed 10.5-11 volts. I also took 2 shims out to tighten up the belt some while we were at our Air BnB as well as put a brand new belt on.

Are these older 911's prone to this? Alternator? or would something having to do with my window switches/regulator cause this? Thanks for any input.

theiceman

i would wire in a voltmeter, lots of people do this, even just one of those that plugs into the lighter socket. you should be charging at 13-14 volts while running , if its lower than that something is likely wrong. it is also possible you are OVERcharging in the 18v range periodically and that will cause your radio to go into overvoltage protection and shut off , and can damage your battery. as well as boil it and spew acid into your car which is very bad. if you have ever smelled Sulphur or rotten eggs while driving this could be it.

other than that you can connect an ammeter in series with your battery while stopped to see what current is drawing, should be just a few milliamps to run the clock and maybe keep radio settings alive id say 20-30 . if its off the charts start popping fuses till current draw comes back down, then you will know which circuit is your issue.

wildcat077

The long and simple way is to connect an ohmmeter ro the battery and set it to milliamps and remove one fuse at a time to see which circuit is drawing power from the battery , eventually you’ll pinpoint the faulty circuit … it’ll be a long process but it’s free and it works.
Keep us posted !

Cheers
Phil

theiceman

its an ammeter ( current measurement) and it has to be in the circuit by removing one post off the battery and inserting the meter in. .... but yeah ... the only caveat is that if it is a bad diode in the bridge rectifier in the alternator it will not be cured by popping fuses, but one step at a time...

wildcat077

Is that what they’re called ?
Mine is an orange SnapOn unit that i use once in a while , actually i can’t even remember where it is in my shop … lol
I think i had to connect a clamp to the positive cable and it would detect the current loss in milliamps, either way it worked well.
You can probably rent/ borrow one from one of the large auto parts outfits.

Cheers
Phil

theiceman

oh yeah current clamps are great , but not everyone will have one, they can actually detect the current going through the wire. quite spendy .. you must be a high end dude.. lol

wildcat077

I use high end tools 🙃🙃🙃

That’s one area where i don’t cheap out !
We had a SnapOn guy at work for many years and at the time it could be purchased through payroll deduction with a great discount, so i accumulated
quite a collection of SnapOn and Blue Point tools !

Cheers
Phil

Spyerx

Wonder if your voltage regulator/alternator and/or battery are getting flakey. I would replace the battery if it's more than 5 years old. Get an H6 AGM. Make sure the ground, and all connections are tight.

I have a 12v cigarette lighter I'd use on my old 89. The charging system on these is kind of weak as it is but even with everything on in the car and crusting you should see over 12v.

Now, not turning over can be a few things. On my 71, it was due to the starter. The trigger wire for the starter solenoid runs from the key all the way to the engine harness. I dont recall the switch trigger on the G series compared to the F series but I believe its similar and wasn't changed until the 964. So it's possible your solenoid is not getting enough current to activate it and start the car.

This could be a bad starter, solenoid, or the voltage on the trigger wire on the solenoid. A fix here (it's common and this removes the load that comes from the ignition)is to put a fused relay on the trigger. I have this on my 71, the starter cranks with authority now. Ironically VW had the same problem and there are kits out there for this.

systemsc

Actually, an AGM requires a higher charging voltage (>14.5), than the typical lead acid battery. This becomes problematic on pre-'80s 911s and with Bosch alternators (964/993 - typical output ~ 13.8V).

Spyerx

Yes this is a good point, I used an AGM on my late G series car w/o issue and it lasted many years. AGM has the advantage of not turning into a corrosion source...

I still think OP should look at charging performance (Measure at battery off, idle, under load), but also investigate the starter. My starter issues happened when hot... what he describes sounds like starter/starter trigger.

BTW, phantom draws on the 89 can be traced to the light and power window power that shuts off when a door is opened. It didn't sound like OP has a phantom draw though.

systemsc

It's the starter solenoid via the yellow wire from the ignition switch (#50).

alfetta

I had the same issue on my 85. It turned out to be an aftermarket amp (under the seat type) that stayed in some standby mode.

millermotor

Thanks everyone for the input, I somehow never received email notifications on these replies do I didn't see everything until now. Battery is an AGM one. Maybe a year old. There is an aftermarket stereo in the car that was there when I bought it. I will give these suggestions a whirl and see what I find.

Spyerx

Yes thats the one. I put a relay on mine, would rather ‘less’ current going through the switch…

Mlrjr

My 89 did exactly the same thing…..voltage regulator was the culprit.