I checked for voltage drop at the headlights as recommended with the following results:

12.47 v across the battery
10.81 v front left battery to headlight with lights on
10.67 v front right same setup

I cleaned the connectors and turned up the idle a little to keep things going.

significant loss-I read the article about installing relays-has anyone done this and how did it work?

Should I assume that I am seeing a similar drop in the ignition circuit?

If I rewire the engine compartment where can I get good matching connectors and plugs to do a clean job?

Dave (only motors in the daylight)

YUCK!

Means you are getting only 53% of the light out of your headlights that they would be producing at 12.8v. (As an aside, I hope this was not an engine-running test, because if it was, your 12.47 across the battery is severely low and indicates your charging system isn't working).
Cleaning up the connectors is a good idea. Turning up the idle is a band-aid.
I did it and it works great.
Don't assume anything...measure! What you've found out so far is that your headlamps are being starved. That might be due to high resistance in the headlamp circuit, high resistance in the main feed (A1-A, the thick red wire that is held to the firewall connector by a through-bolt rather than a snap-on connector), and/or high resistance elsewhere in the system. It makes sense that generally high voltage drop could reduce ignition primary voltage to the point where the spark is of poor quality, causing the stall-out. But we won't know for sure until more tests are done.

Start the engine and let it idle, with the headlamps off. Put your voltmeter across the battery. You should see at least 13.3 volts.

Now, with the engine still running, put your voltmeter positive lead on the input side of the ballast resistor and the voltmeter negative lead on the battery negative terminal. You should see no more than about 0.1v less than what you saw across the battery.

Now, put your voltmeter positive lead on the output side of the ballast resistor and the voltmeter negative lead on the battery negative terminal. What do you find?

Now, put your voltmeter positive lead on A1-A (see above) at the firewall connector, and your voltmeter negative lead on the battery negative terminal. What do you find?

Now, put your voltmeter positive lead on the alternator's output (B+) stud, and your voltmeter negative lead on the alternator's housing. What do you see? Now, move the voltmeter negative lead to the battery negative terminal and keep the positive test lead on the alternator's B+ stud. What do you see?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanx for the step by step check up-here are my results.

What do you think???

Start the engine and let it idle, with the headlamps off. Put your voltmeter across the battery. You should see at least 13.3 volts. >>>>>>13.83v<<<<<<<<<

Now, with the engine still running, put your voltmeter positive lead on the input side of the ballast resistor and the voltmeter negative lead on the battery negative terminal. You should see no more than about 0.1v less than what you saw across the battery.>>>>>measured to ballast resistor jumper (HEI) 13.2v<<<<<<<<<

Now, put your voltmeter positive lead on the output side of the ballast resistor and the voltmeter negative lead on the battery negative terminal. What do you find? >>>>>>see above<<<<<<<<<<

Now, put your voltmeter positive lead on A1-A (see above) at the firewall connector, and your voltmeter negative lead on the battery negative terminal. What do you find? >>>>>>>>>>13.83v<<<<<<<<<<<<<

Now, put your voltmeter positive lead on the alternator's output (B+) stud, and your voltmeter negative lead on the alternator's housing. What do you see?>>>>>>>>13.95v<<<<<<
Now, move the voltmeter negative lead to the battery negative terminal and keep the positive test lead on the
alternator's B+ stud. What do you see?>>>>>>>13.95v<<<<<<<<


And, for the men and women out there who are or were in the US military: Thank you for your service!!

All your test results are "very acceptable" to "excellent"; I don't see any systemwide voltage drop that could be causing your problem. Back to square one, as it seems!

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Year one sells an entire harness for the engine compartment that is pretty priciey but will replace everything properly. I would follow Dan's formula, and see where the problem is before I bought anything. It may be that the voltage drop is in the headlight switch, and not in the ignition,although it is likely that this problem is throughout your wiring. The greatest resistance tends to be in the bulkhead connector which has been collecting road salt and spray for 40 years. You can replace these one at a time, and make a serious improvement in the overall performance of the car. When I went through this little exercise 5 years ago the mileage on my '69 improved from 13 to 18 MPG. All I bought was new wire, and new connectors, and made my own harness. It was fun to see how each change brought the voltage drop down. If you can get the voltage drop down to .5 volts you will be making a marked improvement to the system. If your alternator is putting our only 12.8 volts, check the resistance of the wire that goes from the regulator to the alternator. Get that replaced first.

Oh yeah, the relay thing with the headlights is good too, but get the wiring checked out first. I picked up a relay board from a junk car which now resides under the hood of my '69. It runs more than just the headlights,it turns on the ECU for the EFI, the AC, and the fans as well.

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69 Dart Swinger, 230 ci slant, t-5 five speed, intercooled turbo, 4 wheel disk brakes, tubular upper control arms.