por4ever

The last two times I have started the car the volt meter reads 12V after a couple minutes it reads about 13.8. Today I confirmed it by only getting 12V while the car was running and using a multimeter checking between batt + and a couple bare metal points in the engine bay, motor and chassis. The master warning light is very faintly flickering as is the light under the 10V mark on the volt meter in the dash. The battery does have some new corrosion on it but i do appear to have good ground.

I read in a previous post the mark under the 10V is an alternator warning light.

Should I be looking at the battery or the alternator? In the past when I have had an alternator fail it was very obvious. This is my daily driver so I need to get it 100% ASAP. TIA

por4ever

I just ran the car for about 10 min and drove around the block but the volts stayed at 12V. I have no master warning or voltmeter lights lit.

eniac

Your voltage regulator could be on it's way out.

Chris Prack

Why don't you use your voltmeter to measure voltage drop? Start with the ground circuit.

I will work on your next question while I wait.

por4ever

Chris - Which voltage should I be measuring? When the car was off I got a consistent 12.7 across the terminals and from the + to engine and chassis. From - to engine and chassis is about a .7V difference. Is there a better test point I should be measuring from?

Eniac - I have been trying to find the symptoms of a bad regulator but Google comes back with very little.

Chris Prack

Use the DC volt scale. Place the positive lead on the negative cable end and the negative lead on the engine somewhere like the cam housing. You want to see less than 200mV. Anything more than that is going to cause any number of problems.

por4ever

I got 0mV on the cam housing, intake manifold and a nut on the shock tower with the car off.

Chris Prack

Do it with the car running.

por4ever

5mV at the same test points as above. I just checked the owners manual and it says the light on the voltmeter is an alternator warning light. It should come on when I start the car then shut off when the engine is running. It does not light at all now. The master warning lights when I star but then goes out when the car is running. I have started the car about 5 times now and the battery seems to be holding ok instead of running down. Is there some circuit that tells the alternator to start charging depending on engine speed? I am perplexed.

GuyKeefer

My car starts out reading 14V when I first begin driving, and then will drop down to 12V until I park the car and restart it. I had a problem with an old loose alt belt and had that replaced, but I still see the same readings. All I know is the car does not run down the battery and it starts whenever I need it too, so I am not too concerned until something worse begins to happen.

-GuyKeefer

por4ever

Mine did that too. As I understand it the alternator should put out about 14.5VDC until the battery is recharged from the start then drops down to about 13VDC when the battery is charged. My problem is I am reading battery voltage which is 12VDC. Whenever I have run on battery the car ran very poorly until it would finally sputter out. But that was in my 914 but that has much lower power requirements.

88BlueTSiQuest

First, check the alternator light. It's at the bottom of the volt gauge just like the oil pressure light. Turn on the ignition, it should light up.

If it doesn't light, then go ahead and start the car. If the voltage gauge is only reading ~12 volts, gently rev the car to 3k and see if the gauge suddenly pops up to ~14 and stays.

If this is the case, it's an issue with the bulb check circuit. Either a bad bulb, or something that is in line between the alternator and the bulb. I had this issue on my car, and it's only been 'temporarily' fixed until I can troubleshoot it correctly. I was able to take a wire from the bulb check light, and connect it directly to the alternator(blue wire) to regain factory operation.

I need to look through the factory schematics to see where this circuit is, whether it's a relay issue or something else in the fuse box, but I'm sure that is where my problem is.


If your light worked, and you still have a voltage issue, it's probably a voltage regulator. I'd say it would be time for a new alternator(only a matter of time before the brushes go).

88BlueTSiQuest

The alternator will always put out ~13.2 - 14.4v, our cars are closer to ~13.4. The only thing that'll change with load would be the output amperage, until you 'tax' the alternator and can actually start pulling down the voltage(i.e. Turn on lights, heater, etc, and the voltage will start to drop). Think of it like your wall outlet, there's always going to be 110v there whether something is plugged in or not.

Battery charge level will have no effect on what the alternator is putting out unless the battery is weak and is pulling down the alternator.

por4ever

WOO HOO! I started it this morning and after warming up a few minutes I reved it to a little over 3k and the voltmeter popped up. Where exactly did you bridge the wires? I don't really want to go tearing into my dash today.

por4ever

I was trying to trace it on my schematics too but it connects to things like the alarm and Relay 15 whatever that does. I did swap that relay with the one next to it but no change.