Voltage Reg or Alternator replacement

GRG1911 · 05-10-2003, 08:57 PM

I have a 80 SC...

When I put the voltage meter to the battery it reads 12.5. When the car is turned on the red alternator light and OS2 lights come on the meter drops a little 12.2/12. When I pop the the gas pedal the alternator light goes off and the meter reads 14.

I beleive the voltage regulator has been updated to the internal model. When I look on the back panel by the engine. I cannot tell which little box is the external regulator if it is there. Does anyone have a picture of exactly where it is?

What is causing this problem? What parts should I replace?

MotoSook · 05-11-2003, 03:46 AM

first guess..from a very tire head...need new alternator.

Face · 05-11-2003, 06:08 AM

George,
We need a little more info to help fully diagnose your problem. You should hook your voltmeter up to the system through the cig. lighter (you can buy a cheap lead at Radio Shack designed for this) and monitor while driving. Test the system at idle, 3k RPM, and then again with a load on the system (brights, A/C, defrost etc). While you drive just monitor it for spikes or anything off, it will fluctuate a bit normally.

I don't have an external VR but it should be on the left side of the engine wall, I believe.

Pulling the alternator isn't a difficult job and you could get it bench tested at a local alternator shop. Most can have it rebuilt or you can buy a rebuilt (less costly) or brand new (expensive) alternator. VR's are about $60 from our host.

Let us know what you come up with - it could be anything from a bad ground, bad alternator bushing/diode, to a faulty volt regulator.

Hope this helps a bit!
Cheers,

jmohn · jmohn's Garage

I'm not sure I understand what you think is a problem.

Quote:

Originally posted by GRG1911
I have a 80 SC...

When I put the voltage meter to the battery it reads 12.5.
This is normal (I assume the engine is not running).
When the car is turned on the red alternator light and OS2 lights come on the meter drops a little 12.2/12.
Again, normal (with the engine not running).
When I pop the the gas pedal the alternator light goes off and the meter reads 14.
I assume at this point the engine is started and running, the 14v is normal also (a bit higher than mine, mine shows 13.1-13.4v, at idle). If your concern is the necessity to rev. the engine slightly to get the light to go out, it's not that unusual. I assume once you've rev'ed the engine and the light goes out, it stays out. If the light comes back on when the egine drops to idle, it's probably time to rebuild the alternator.

I beleive the voltage regulator has been updated to the internal model. When I look on the back panel by the engine. I cannot tell which little box is the external regulator if it is there. Does anyone have a picture of exactly where it is?
If your regulator has been chaged to the internal model it's inside the alternator (this means you have an "up-dated" alternator) therefore you probably don't have the external regulator which would be mounted right next to the CD box (toward the front of the vehicle).

What is causing this problem? What parts should I replace?

I'm not sure you really have a "problem". As an earlier post said, connect your VOM so you can monitor the alternator while you're driving, if it stays above 13v and doesn't continually exceed 14.5v, you're OK.

Good luck,

Jerry M
'78 SC

Face · 05-11-2003, 07:22 AM

George,
When you turn the key to the "on" position, before cranking, the alt. light should illuminate. Then once the car is cranked, the light should go out - I'm reading your post as - the light stays on after starting the car until I rev the engine up above idle. Is this true?

Joeaksa · 05-11-2003, 07:45 AM

George,

There are several diodes in the alternator. One of these usually controls the "idiot" light that is staying on in your car. If you blow one of these diodes but the alternator is still charging and able to hold its voltage when you load the system then you can still drive the car but its usually a matter of time before you will need to overhaul the unit.

This can happen when you jump the car or give someone else a jump or if anyone welds on the car with the battery connected or it can just fail. Bottom line is if the system holds 14 volts while loaded up (window heat on, A/C on, etc) then its working properly.

Without a volt meter in your car (I put one in the dash) and the red light staying on you have no idea if its failed while you drive or not. Other problem is that the red light is also the one that lets you know your fanbelt has broken and you are quickly cooking your motor with no cooling air. For this reason alone you should repair the problem.

Joe

Joeaksa · 05-11-2003, 07:48 AM

stlrj · 05-11-2003, 09:20 AM

George,

If your idle is too low the red light will come on. So check your idle rpm so it isn't too low. 14V at rpm sounds perfect...nothing wrong with your alternator.

Your battery might be low in need of a charge.

Joe

pwd72s · 10:30 AM

The numbers looked good to me...I recently picked up a plug-in volt meter. Plugs in the cigarette lighter, gives a digital read ot as you drive. Cost more expensive than the male plug wired to a cheap multimeter tho., about $70 delivered. It also had the problem of not fitting tightly because of the larger German lighter plug...easily fixed with a bit of milk jug plastic & electrical tape. It's range is 8 to 25.5 volts, has a recall button that gives the highest voltage reading of a run. Made by Norskog Performance, Oxnard, California. Phone 805-483-2411. What I like about it is that my dash remains original, yet I have a full time volt meter any time I want...

GRG1911 · 05-12-2003, 10:37 AM

The problem that I am having is once the car is running the alternator light goes out after I rev the engine, but the OS2 light stays on and does not go out.

If I replace the alternator will it resolve this problem also.

targa80 · targa80's Garage

The O2 sensor has a reset switch on a module behind the odometer. After 30K miles the O2 sensor light comes on and needs to be reset. This is to indicate that you should change the O2 sensor. If the idle rpm is to low the alternator light will come on. If you blip the gas and it goes out and stays off after the idle settles down then you don't have a problem with it. If the light does come back on when the idle settles then the voltage regulator or the exciter diodes in the alternator are starting to go. Do a search on Idiot light/ alternator. there are threads with with more discription of the problem.

targa80 · targa80's Garage

I believe the original handbook for the car describes how to reset the O2 sensor switch. If not then it is in the Haynes manual.

GRG1911 · 05-12-2003, 12:45 PM

I reset the OS2 sensors by pushing the white button behind the speedo and that the light remains on.

Any other suggestions....

Thanks
George

targa80 · targa80's Garage

I just looked at the 1980 schematic for the O2 sensor light It receives its 12 volts from the oil temperature indicator and it is connected through the relay contact of the milage counter to the oil temperature indicator ground. Resetting the counter after the 30K miles would open the relay contacts and remove the ground. It is also connected to the generator charge indicator light thru a diode in the milage counter. When the ignition key is on and the engine is not running the generator and O2 lights find a path to ground through the voltage regulator and come on. with the engine running the exciter diodes in the alternator provide an equal voltage to the voltage regulator removing the ground path for both lights.

GRG1911 · 05-12-2003, 07:49 PM

Thanks Pat. My guess it is a burnt out diode. I will replace the alternator and voltage reg in a couple of weeks to eliminate these problems.

George