"Pulsing" voltage, RPM drop with load.

[Mattax]

Measurements at battery terminals, engine off.
Everything off 12.6V
Headlights on 11.9V
Brake lights on 12.0V
Brake lights and head lights on 11.8V

Maybe a slightly discharged battery but OK.
Your car has side marker lights so lights on the load is slightly higher than a '67. Therefore that they pulled the battery down a little more than Dana's is not surprising.

Measurements at Cigarette lighter , engine off.
Everything off 12.4V
Headlights on 11.2V
Brake lights on 11.9V
Brake lights and head lights on 10.9V

Same as above. Resistance in the circuit. Since you've interconnected the battery and alternator feeds, the resistance is either shared (such as battery to stud on relay) or its in both the alternator and battery feeds to the main splice.

Measurements at Cigarette lighter , engine cranking.
Everything off engine cranking 10.6V
Everything off engine running at idle 14.7V 850 RPM otherwise car was last running yesterday.
Engine running at idle headlights on 14.0V
Engine running at idle brake lights on 14.5V
Engine running at idle headlights and brake lights on 13.0V

Need to be looking voltage drops and checking for whether the voltage follows the rpm.
Going from 14.7 to 14.5 and 14.0, is OK but then the big drop to 13.0 doesn't make sense (if rpms were the same). Another variable we don't know is the battery charging rate. But it should have been highest immediately after starting and then drop quickly.

Voltage at alt is 12.75V but I measured this after warming up the car. It was also 12.75 at battery

??? Do you mean after you shut the engine off?

Remember that I ran a 10ga wire from alt output to starter relay with fuse link.

You should get the exact same results with the wire removed. The only difference is the ammeter will show the amount the battery is charging when the engine is running.

 

[JoePole1]

??? Do you mean after you shut the engine off? YES. I should have stayed that.

"Need to be looking voltage drops and checking for whether the voltage follows the rpm.
Going from 14.7 to 14.5 and 14.0, is OK but then the big drop to 13.0 doesn't make sense (if rpms were the same). Another variable we don't know is the battery charging rate. But it should have been highest immediately after starting and then drop quickly."
Rpm's were the same. I'll recheck my readings again next chance on Friday. Had to pull the ashtray but no big deal.
I will also check voltage at different RPM 's.

When I had the ammeter hooked up as stock I remember it being at 70% when first started and then settle to 50% pretty quickly.

Thanks for your help.

 

[Mattax]

The 72 ammeter I think is still 40 amps to 40 amps.
So if you saw deflection toward charge about 20% from center, that's about right.
Then it went to center when there charging was complete.
If the alternator can't supply the power, the ammeter needle should go toward discharge as the battery takes over.
It should have done that even with jumper you put it on. The path from the battery through the ammeter is shorter and normally less resistance than following the jumper to the alternator stud, then to the bulkhead.

If you have long enough leads on your meter you can measure voltage difference between the alternator stud and other connections directly. But for first checks I like to just measure voltage to ground.

When there is no flow, the voltage will be the same everywhere. So with everything off, the alternator stud, battery positive and all the wires in between should be at the same voltage even with a bad connection.
Its just like pressure. If there is 12.8 psi on one end of a closed pipe, its 12.8 psi throught the pipe.

It doesn't matter if inside the pipe there is a partial blockage. It's still 12.8 psi throughout.
If we could look inside, the pressure on both sides of the blockage would be 12.8.

Connecting that same pipe to an air gun or an impact wrench and lets see what happens to the pressure.
There's still 12.8 psi supplied, but on the other side of the restriction the pressure is lower. The more air being used downstream, the more the pressure drops.

 

[JoePole1]

Thanks Mattax. I am going to guess here and say that you were an instructor or teacher in your professional life. If not, you should have been.

 

[Dana67Dart]

When I had the ammeter hooked up as stock I remember it being at 70% when first started and then settle to 50% pretty quickly.

That is exactly how mine works.

Thanks Mattax. I am going to guess here and say that you were an instructor or teacher in your professional life. If not, you should have been.

I second the motion!