Help w/ battery draining or alternator not charging

[timmy2]

Sherwood, read the post above yours.
He fixed it by allowing the alternator cable to make contact with the battery cable. It was mounted to the wrong terminal on the starter.

To the OP, yes it is counterintuitive to connect red to black in North America. Brown is ground for most European cars.
In actuality the way it was hooked up, the only time the alternator was charging the battery was when the starter was engaged.

[911pcars]

Originally Posted by timmy2

Sherwood, read the post above yours.
He fixed it by allowing the alternator cable to make contact with the battery cable. It was mounted to the wrong terminal on the starter.

To the OP, yes it is counterintuitive to connect red to black in North America. Brown is ground for most European cars.
In actuality the way it was hooked up, the only time the alternator was charging the battery was when the starter was engaged.

Yeah, I noticed the solution a few minutes later. Thanks. Glad the starting issue is resolved. The system conductor puzzle looks formidable, but one wire at a time and pretty soon, it's done.

To the OP, make it look neat, as if it came from the factory..... and take notes.

S

[timmy2]

Your red cable was mounted to the other side of the switch in the pic below of the schematic. (Opposite side of 30)
The black comes from the battery positive, the red from the alternator to terminal 30 in the photo.

[sugarwood]

Originally Posted by timmy2

I think I barely see the be red cable from the alternator connected to the wrong large bolt. Both red and black connect to the same terminal as the black is currently on.

Can you circle what your eagle eyes saw?
I see no red cable !

[sugarwood]

Originally Posted by D85James

Yahtzee! Wouldn’t have thought the red and black thick cables go to same post on the solenoid. Guess when whoever did the swap they wired her up wrong. Light comes on dash with key to run, light on start then goes off. Cigarette lighter shows 14.3V while running 12.8V with car in accessories switch. Thanks Pelicans for the support

For the archive, can you post a before/after photo of the correction ?

[timmy2]

Lol, just zoomed in on my phone and saw what is circled.
Fat black cable was prominent in front lower area, searched for alternator cable.

[Walt Fricke]

This leaves me with a loose end. With the alternator as a second current source if attached to the upper screw terminal, wouldn't the alternator current cause the starter motor to turn? Because it would bypass the relay? Might go unnoticed because the relay would not also cause the starter gear to move out to the flywheel ring gear? That might accelerate the draining of the battery when driving?

[911pcars]

Originally Posted by Walt Fricke

This leaves me with a loose end. With the alternator as a second current source if attached to the upper screw terminal, wouldn't the alternator current cause the starter motor to turn? Because it would bypass the relay? Might go unnoticed because the relay would not also cause the starter gear to move out to the flywheel ring gear? That might accelerate the draining of the battery when driving?

Walt, If I understand your question, that battery/alternator terminal on the solenoid is only connected to the starter motor when the solenoid is energized. At all other times, it's just a junction point.

Sherwood

[Walt Fricke]

Sherwood - agreed. But it seems someone connected the alternator wire to the other screw post, which I believe connects directly to the starter windings or whatnot, and is supposed to be hot only when the solenoid/relay directs power to it.

[911pcars]

Originally Posted by Walt Fricke

Sherwood - agreed. But it seems someone connected the alternator wire to the other screw post, which I believe connects directly to the starter windings or whatnot, and is supposed to be hot only when the solenoid/relay directs power to it.

Walt. Ahh. Understand your description now. Wouldn't it be easy enough to confirm the starter motor is either at rest or rotating with the car on a lift? Maybe even hear it at some threshold engine rpm, and with a voltmeter lead attached, voltage viewable? Starter motors are quite noisy, even when spun unloaded.

At any rate, merely piece together the circuit as designed and it should work, but it's interesting what happens when a circuit is randomly connected.

Sherwood

[Walt Fricke]

Happily, the blunder someone made has been found, fixed, and we have a happy camper.

My reward from noodling problems and reading the thoughts of others is a better understanding of the systems. The solenoid is a very high amp relay. Some starter systems also use it to lever the starter gear out to engage the flywheel ring gear. I'v never had one apart, and so don'r recall if just turning the motor causes this motion, or if a lever does it.

My former VW van developed a sticky starter. I would get an arm in there and short the two big posts together. This would spin the starter without turning the engine. Usually the engine would then start. Probably a bad commutator segment? Bit of a pitn, and I ran wires to the outside of the car to short there - until I replaced the starter - the right fix.

[7783911]

Did you confirm charging at 1500 rpm. I ve seen where if the alt lamp is incorrect the exciter on the alt doesn’t get triggered..change the bulb and retest at 1500 rpm to see if charging.?

[jpr2013]

Hey folks, this is my first post. I bought the 78 SC with the 3.2l engine swap from James about a month back. I've been positively chuffed about the car, it's pretty much exactly what I wanted--a driver with the 3.2 and a nice sport exhaust that'll give me something to work on for the next few years. I'm pretty new to wrenching, but building up a project list and tools and starting to roll up my sleeves and get to work. So far I've adjusted the heat valve box (was previously stuck open and sending scalding heat to my feet at all times—not fun in Houston on the edge of summer!), changed oil on two of my cars including the 911, done plugs and coils on my Boxster S, and started the painful task of pulling old window tint from the 911. I've also got a list of projects and some parts, including new door cards, door stops, door stop reinforcement, and stripping out the back seats and shelf. But before I can get to the fun stuff, I've got a problem.

Last weekend I discovered I seemed to be having the opposite problem that James had: too much juice being sent to the battery. Came home from a drive and battery was bubbling and smelling bad. Thankfully, nothing ignited in my garage. I finally confirmed it tonight with a volt meter (had to wait for one from Amazon and the first one got lost), that was reading around 18V with any kind of revs at all and that's even with the lights on and running a radar detector.

Now, from what I gather on the forum, the answer is generally that the voltage regulator in the alternator has gone bad. But I know from James's earlier posts and talking with him that he had the alternator checked and put a new voltage regulator in last October. So I'm a little concerned that it could be something else.

So, should I just replace the voltage regulator per the general wisdom about this issue, or given how relatively new the alternator is and that it has a new voltage regulator, is there something else I should do in terms of diagnosis before just replacing the part?

[Walt Fricke]

My one experience with an overcharge was resolved by replacing the VR. I had a new VR fail on me within a couple of months once, though it failed in the usual way - no charge.

Not much else to go wrong, as all the key connections are right there in the alternator. Bad grounds usually mean voltage drops, not boosts. Maybe someone has better informed ideas about what, other then the VR, could cause this.

[mysocal911]

Originally Posted by jpr2013

So, should I just replace the voltage regulator per the general wisdom about this issue, or given how relatively new the alternator is and that it has a new voltage regulator, is there something else I should do in terms of diagnosis before just replacing the part?

An overcharging alternator can be problematic especially for a 911 3.2 engine with the Paris-Rhone internal regulator.
The overcharging alternator can damage the DME ECU, destroying the fuel injector's driver circuitry.

[jpr2013]

Thanks for the responses, guys. I’ve ordered a replacement regulator from our host. If anyone else has thoughts, they’re very welcome.

[darrin]

personally, I'd have the entire alternator and regulator assembly "gone through" by a (preferably local), old-school alternator repair shop -- that way, you'd also be comfortable that the diodes, brushes, rotor, etc. are good to go, especially given how recently your current one failed.

Also, I enthusiastically echo Dave's point above -- don't drive the car until the overcharging situation is resolved.

[jpr2013]

Thanks, I have not taken it out except for a couple minutes to verify the overcharge. I like the idea of taking it to an alternator shop.

[jpr2013]

Anyone know a good alternator shop in Houston?

[darrin]

found this thread, few years old -- Rebuild alternator in Houston?