Help, last winter I replaced my motor and have been enjoying my car the last week or so but today out of the blue I had a dead battery after driving for a few miles. I jumped it and all appeared to be fine, however on the way home, after dark I might add my lights began to dim, my radio quit playing, but the car continued to run. To make a short story long I was pulled over by the police for no lights and speeding. To make matters worse i didnt have my drivers license with me, but I did have my wife and kids so after a stern warning the officer let me go. Anybody got any ideas on where to start looking for the problem. It is a brand new battery last fall. Thanks

Sounds like the alternator is not charging, have it checked and also check the voltage regulator

Check the charging system. Should have 14-14.5 volts at the battery with the car running at a fast idle. If you have battery voltage or less, its not charging. If its not charging consider changing to a more modern charging system with a internal regulator, very easy to do. Do a search or post back if you need help on this.

I took my alt to the napa store and tested it (twice) it showed good both times. The voltage reg is new (last fall). Is there a way to test the regulator? I dont really want to change the regulator from external to internal. The battery is new (last fall). It was drained after last night but I charged it back to 100 percent. What should I check next?

What should I check next?



This was written by another member, a very good write up on how it works and how to troubleshoot a externally regulated charging system.

I dug this out from before, hopefully it help. If not, just post or send me your questions.

I'll try to provide a simplified explanation of how the externally regulated alternator and regulator work here. This explanation starts from a parked car with engine off state.

The regulator brown #4 wire is connected through the light bulb to 12V whenever the key is in the ON position. The other end goes through a set of points in the regulator and then out the F terminal to the field winding in the alternator. So some current begins flowing in the field winding from this connection. The little bit of current flowing produces a weak magnet field in the alternator and also lights the bulb.

When you then start the car, the weak magnetic field from above begins rotating which makes the alternator producing a little bit of voltage. This voltage is fed from the alternator to the regulator on the white regulator #2 wire. This wire connects to a coil in the regulator and turns on a contact when the voltage goes above 3.2V.

Once the contact turns on in the regulator the #3 and #4 terminals are connected together. Terminal #3 is battery power so this puts battery power on both sides of the bulb and turns it off. This means the brown #4 wire should go to +12V. Also, this connects the field terminal right to battery power but still going through the points.

When the battery voltage goes above a set level, the F terminal is disconnected from the battery power by the points I kept mentioning. Then the voltage drops and the points close again. This on-off cycling happens rapidly and is how the voltage gets regulated.

From the above (KOEO = key on engine off and KOER = key on engine running).
F or #1 terminal (field) - KOEO = #4 slight voltage, KOER = 9-12V typically
#2 terminal (sense) - KOEO = 0V, KOER = >3.2V
#3 terminal (Battery) - KOEO = 12V, KOER = 12V
#4 terminal (light) - KOEO = F slight voltage, KOER = 12V

By 12V above I mean battery voltage, which may be 12V when engine is off but could be up to 14.5V when engine is running.

Check the light: Ground the brown #4 terminal wire at the regulator. When grounded the light should come on. If you don't have a light then skip this test. Test this with the connector off the regulator.

Checking the alternator: Jumper the blue wire F terminal to the battery post on the back. This should make it easily crank out 16+ volts. Next, connect a troublelight between the battery post and the F terminal. The light should come on and you should measure > 3.2V at the other alternator terminal. If it passes these tests, then it's in the regulator or wiring.

Checking the wiring: At the regulator connector jumper the brown light wire (#4) to the F terminal (#1) and you should be able to measure >3.2 volts on the other alternator terminal or terminal #2 of the regulator connector. If these tests pass, it is in your regulator.

When doing these tests, make sure you turn off or pull the fuses for any added electronics that you can. The alternator test can produce enough voltage to damage stuff.

Peter

ok, I checked the alt , its ok. I replaced the regulator and charged the battery. It now starts and idles as normal except the gen light on the dash goes on when it idles. If I raise the RPM's the light goes out until it returns to idle speed then the light comes on again.

It now starts and idles as normal except the gen light on the dash goes on when it idles. If I raise the RPM's the light goes out until it returns to idle speed then the light comes on again.
Did it do this before? Are you using any kind of power pulleys ( smaller crank pulley or larger alt pulley) Problems like this is either, electrical demand is greater than the alternators output, (how many add ons do you have and what amp alternator) the alternators not turning fast enough because of idle speed or pulleys http://www.powermastermotorsports.com/power_pulleys.html
or the alternators on its way out.

I have a March pulley kit on my SB and when I start it cold, the lights dim and shutter but when I rev it they brighten up. Once the engine is warmed up it stops doing this, but I have my problems with the carb and it doesn't idle right but works fine once it us warmed up which is why when it runs better, the lights work better. That's a different story though... Anyway, it's only when the car is idling rough and cold and I do have a smaller pulley set up, so post back if this is the case. If not, couldn't it be something as simple as the connections?

Check the alt. output at idle to see how much volt you have. I have seen some alt's that will check good but at idle a diode being bad caused the light to come on.