« Reply #4 on: September 30, 2024, 10:40:45 AM »
Really sounds like battery. Try starting with voltmeter on battery and watch for drop. Static voltage across the battery doesn't tell you much, but when drawing current you can tell how strong the battery really is.
I agree, sounds like the battery is in the process of failing. Or run a load test on the battery. If you don't have a battery Load Tester, take the car up to your auto parts house and let them test it. Or better yet, take the battery out. Take it to them. They will first charge it up and then load test it. You can ask them to load test it prior to the charge but some seem to balk at that. I've had batteries doing exactly what you say. Reading about 12.4 volts static. Reading the 14+ when running (meaning the alternator and volt regulator is working) and yet starts are sluggish. A load test shows a failing battery or it it "Dinks" to zero, a shorted battery. I don't think yours is shorted as you are still able to mess around and get a start.
Remember the batteries number one job is starting the car. After that the charging system is in "charge" (pun intended).
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1969 Mustang Coupe, 302-2V, auto, air, PDB, Lime-Gold. In the family since 1972
1969 Mustang Mach 1, 428 CJ Ram-Air, Auto, air, PDB, PS, Grabber Orange. Self restored (for the most part).
2008 Mustang GT Convertible. Weekend driver.
Always looking to learn and improve the cars.