The 85 has a 2 year old alternator......We were driving in town and the volts dropped to the low 11's and on the highway high 12's.......I just started it up and it ran at 14.1 as soon as I turned on a/c, headlights the volts dropped dramatically......looks like the battery is about 4 years old

 

Take it to a parts store like Autozone and have them check the battery and altenator. If both are good, you probably have a belt going bad.

 

If the alternator isn't charging the battery your red battery symbol light on the dash will come on. The alternator attempts to maintain 14.7 volts across the battery all the time and it will drop this voltage when the alternator exceeds its rated current . It sounds like your alternator cannot deliver its rated current, or it cannot deliver much current at idle speed. The trouble with car parts places that test your alternator is they don't fully load the alternator and they don't run it through its rpm range and they can't check for oscillating voltage regulators. A discharged battery draws a lot of current from the alternator and this might be your problem. I would first charge your battery up with a battery charger for 24 hours and then check how your electrical system performs.

 

You have charging problems I.E. Belt, Alternator, or my favorite a loose or dirty connection. However, finding a faulty alternator does not mean that your battery is good. To truly diagnoss an electrical problem you should look at the system holistically and troubleshoot the components, that way you know that you fixed the problem without throwing a bucket of money after it.

Good luck.

Mike

 

Go to radio shack and get an accessesory plug with bare wires. You will note they are marked + or -. Now take your voltemeter and connect it to the appropriate wire and plug into cigar lighter. Now take a freind for a ride with the job of watching the voltmeter you hooked up. It should respond the same as the voltmeter on the car and if it does't then you have a bad meter in the car. If the battery is bad the voltage will drop down to below 9 volts on startup. It should not go below 10 and even better it should be 10.5 to 11 volts when starter kicks in. Now you have checked the meter and the battery. I have recently had the experience of having an alt. checked at three different places the same day and all said it was good. That said I went to the service bulletins for GM and found out that they had a problem with alternators that went to ground leaving the car running on the battery. The battery only holds 12 volts so you would see a reading of 11 or 12 volts when this is happens. You should also notice the lights dim and brighten. Also because the alternator is only intermittently charging the battery will show it has a weak charge. The car I tested three times in one day got a new alternator and I have not had any problems since with the battery or lights. I hope this may have provided another insight into what your problem is.