alternator light, goes off after a bit? Options

[eg914]

Help! The alternator light is on bright with the key on, but before the engine is started. It stays on after I start the engine, but is about half bright and pulsing slightly. Then it goes off after I drive about a block. It did this last night when I left work, this morining, and again this evening. I heard a high pitch whine a couple of days ago, but it has gone away.

Is my alternator going south? Anybody else ever experience this type of failure? Is it possible it is the voltage regulator or battery?

Any advice will be greatly appreciated.

Thanks

[bd1308]

If it idles low when cold, I think you're fine.

Mine kinda flickers a tiny bit when its cold, but I'm currently more worried about it dying and me having to crawl under it to do the screwdriver trick on it.

b

[eg914]

This is a new behavior. Up till now it has been working fine. The light was only visible if I had my headlights, brakes, and blinkers on all at once, and then fairly dim. Now it is about half or slightly brighter when the engine is started and running. It seems odd that it goes out after about a block of driving, then doesn't come back on till the next time I start the car.

Guess I am wondering how much time I have before total failure of which ever component is causing this.

[bd1308]

I would also check the starter bolt for the lug where the alternator wire is located and terminated.

there is a nut there that fell off on mine, and I was scratching my head wondering why my alternator just died one day after having the light glow in various shades until I just checked (for giggles) the starter and found everything loose.

b

[eg914]

I'll check the starter wire next. Seems like it turns over fine, don't know if that makes any difference. When your wire to the starter came loose did it affect the starter, or only the battery charging?

[bd1308]

yeah my starter was non-functional.

nix that.

i'd still check maybe though.

Maybe the belt is slipping?

That light lights when the two fields have a voltage difference. Or something like that.

b

[eg914]

I checked the belt and installed a new regulator from FLAPS. It doesn't seem to have changed anything. I guess this means a new alternator. Right now it seems to keep the battery charged, since the light is going off fairly soon after starting. I wonder how long I can run this alternator before it quites entirely. Car is my daily driver, and I hate driving my wife's SUV to work. Only 40 miles round trip, so I guess even if it goes on the way in I should still be able to get home!

[bd1308]

maybe your battery is just plain weak?

b

[eg914]

I thought of that, but discarded the idea. The engine cranks over fine, and the voltage at the battery whith the engine off is about 12.5 volts. It was also 12.5v with the engine on and the alt. light on. I haven't had a chance to check the voltage after the alt. light goes out, but may try to do that tonight. Got a couple of other (non-car) things to take care of first. Gotta go now, may be back later.

[davep]

The alternator light is in the path for current to flow to initially build the field in the alternator. Until the alternator is producing its own power that light will be on. After the alternator builds voltage the light goes out. It is actually a tug of war between the battery and alternator. The battery wins when the light is on, and is losing when the light is off; higher voltage wins. The bulb regulates the current for the alternator, so any replacement bulb must be the correct specification.

If the light stays on a bit after the engine starts, then the alternator is not building voltage properly. That is a good indication it will need to be serviced or replaced.

[lapuwali]

Having the light glow dimly, esp. when you're drawing a lot of current, is fairly common. I've had a number of other cars (Alfas, mostly) with Bosch alternators and regulators that have the light barely glow at night as a matter of course. One of the possible suspects is extra resistance in the field circuit: ignition switch, bulb, D+ on regulator, D+ on alternator. This can be the wrong bulb, but is more commonly corrosion on the connectors somewhere. Having the light stay on until you rev the engine up a tad the first time after you start it is also very common. I've driven cars for years that did that. In short, this isn't necessarily cause for panic.

12.5v engine off is good. With the engine running, you should see 13.5-14v at the battery terminals. If you do, the system may be getting a bit cranky, but is still fundamentally OK. If you see less, than it's time to have the alternator rebuilt.

[rcrgrl]

could it be a short, or a loose ground somewhere causing a slight drain?

[eg914]

Thanks for the input. I tried a new solid state regulator, and the light stayed bright and steady even driving around the neighborhood. I put the old style bosch regulator back in and the light is dimmer. Didn't drive around the block to see if it goes out. I'll find out tomorrow when I drive to work. Seems like the solid state regulator is less tolerant of sub-standard performance from the alternator. I will check the voltage at the battery with the light off (hopefully) tomorrow.

Looks like I'll be looking for an alternator in the VERY near future. Being the CSOB that I am I will probably drive it until it fails conclusivly. At least I don't need my lights for the summer commute!

Thanks again to all, this site always seems to provide the answers I need.

[Dave_Darling]

Check the fuses under the dash. Clean them up--#8 or #9 is in the path for the light, which affects the charging system. Clean up the fingers that hold the fuses as well. A wire brush and contact cleaner are your friends.

A lot cheaper and easier than replacing the alternator. Even if it doesn't fix the problem, you haven't lost much.

--DD

[eg914]

Drove it to work today, and the light goes dimmer as rpm goes up. Over about 3500 I can barely (my imagination?) see the light. Oddest thing is that at idle, when I step on the brake or turn on the blinker the alt light gets dimmer! Guess I will be checking fuses and connections Saturday morning. Sounds better than pulling the alternator.
Hope I find something easy and stupid to fix.

Thanks again

[newto914s]

eg914, I just wanted to add, when you do get around to changing out that alt. Make sure to check out this classic thread, WARNING!-Bosch Rebuilt Alternators!!
It's kind of a pain to get that badboy all hooked up thanks to the mid-engine layout, not something you want to do morethan once. If not careful, some rebuilds sort easly to the air guide cover, I fried two Alts and almost my car, before reading this thread. Buena Suerte
Samson

[eg914]

Now the alt light is off when the key is turned on, then flickers bright as the engine turns over, then goes dim until the rpm goes up. Didn't have time to check fuses and such this weekend, got stuck doing computer stuff. Battery seems to be charging, so I am not going to panic yet! (IMG:style_emoticons/default/smile.gif)

[davep]

Based on this info, I'd be checking the circuit feeding the lamp. There many be enough of a trickle to start the alternator without lighting the lamp then, as the engine starts turning over, the alternator is generating enough voltage to back feed the light (it is only supposed to oppose the battery voltage at the lamp resulting in no current, thus turning off the lamp at this point). I'm thinking the ignition switch may be at fault. They do strange things as they start to fail. Replacing them regularly (say every 10 years or 100000 miles whichever comes first) is good preventative maintenance. Always keep a spare somewhere.

[eg914]

davep,

Looking at the wiring diagram, it looks like fuse S9 is fed through the 2.5mm wire from the ignition switch. Your theory is that the connection at the fuse or at the ignition switch should show too much resistance?

If the ignitions switch is failing, are there any "typical" signs I should be looking for in addition to the alt light shenanigans?

Thanks again

[eg914]

Finally spent some time in the garage. My voltage measured at the battery terminals is the same at all times, engine off, at idle, or reved up. Two different VRs give same result. Sad thing is that the alternator is only a couple of years old.

I noticed a whinning for a few days just before the light started acting up. Guess I'm going to have some fun