First regulator in alt went out, replaced it and the battery because it was 6 years old. Started fine for about a week the the starter solenoid just clicked. Car has 270k on it so replaced the starter. Fine for about a week the no start again, no crank. Checked for a draw, no draw?!??. With battery cables connected, battery at 5 1/2 volts. Disconnected the negative battery cable test battery again12.6 volts, touch negative battery cable to battery, 5 1/2 volts. Replaced the negative battery cable yesterday, battery at 12.6 volts...problem fixed! Or so I thought until this morning, same problem!!! The only thing I haven’t had a chance to check, yet, is the ignition switch. Any ideas please!? It’s my daughter in laws car and I’m trying to get this figured out!! Thanks in advance for any help!!

 

anyone??

 

Although the ignition switch can fail after several years, what you are describing is a bit different.
With no load the battery reads fully charged, you place the battery connections from the car to the battery, the voltage instantly drops.
I would say get an ammeter to check the draw, but if the battery instantly drops this much voltage the cables should be getting fairly warm fairly quick if left connected at this observed voltage drop.
If the cables are not getting warm, then I suspect your newish battery has a fault. Have it load tested.

 

Yesterday I put one of my meters on the battery, and put my other meter positive to the s terminal on the starter and the other lead to ground. 12.6 volts at battery and when turning the ignition to start only got a little over a volt at the s terminal and the battery was at 11.5 volts simultaneously. I’m going to test at the ignition switch plug tomorrow and see what I get. Thinking it’s a short to ground at the ignition switch?