Old case still vexing me

[MattCatlin]

Good charged strong battery. Good bat terminals. Reads 12.6 volts at starter. Wont crank. Appreciate anyone willing to watch video and help diagnose. Maybe I should replace ignition switch https://m.youtube.com/watch?v=4NMTtY-etSU

 

[JDIH]

Time to get out the old fashioned test light. Make sure the main lead and small wire going to the solenoid don't lose power UNDER LOAD. Also do the same with the starter body to make sure it's not losing ground UNDER LOAD. Checking under load is very important because you can get enough current to make it look good just sitting there, but not be capable of carrying enough amps for the starter. If that all checks out your new starter is bad.

 

[K-Mo]

In many cases, the solenoid also acts as a switch and has to be FULLY engaged to apply power the the starter motor.
Attach a voltmeter to the solenoid excitation terminal, engage the starter switch and check to see that battery voltage remains on the terminal.
If voltage is lost through he switch and/or cables, the solenoid may not stay fully energized to apply power to the starter motor.
K-Mo
You could also try, try bypassing the starter switch and cables by applying battery voltage directly the the solenoid excitation on the starter.

 

[used red MN]

I agree with everything JDIH said. Your cheapo jumper
cables get hot because they just do not have a large
enough conductor to carry the amps to spin the
starter. Using the cables this way you are carrying the
full load of the starter. When you are jumping to a
battery the cables only carry the amps that assist the
stored energy in the battery of the machine you are
jumping. If you have adequate power at the terminals
checking them as suggested when trying to start
unfortunately it sounds like your received a faulty
starter.

 

[Steve@Advance]

When a starter rapid cycles like that, it's starved for amperage. The solenoid closes, the power is insufficient, so the solenoid drops out, as soon as it opens the connection, the voltage jumps back up, the solenoid closes, the cycle repeats.

You'll need an analog volt meter or a test light.

Start with your volt meter or light directly on the battery posts (not the cable ends). Take the voltage reading while trying the starter. If the power drops to near zero, the battery is bad. If the voltage is good, start methodically moving one test lead at a time, testing under load, until you track down where the drop is.

As you saw happen in the video, it can start cranking at any time, be careful!

 

[rustred]

just because you cables look clean dont mean they are good. they can corrode from the inside and cause just what is happening there. and reading 12.6 volts at starter dont mean it will start either. you need to get good amps to the starter. hook up some heavy cables to the starter from a booster truck and try it. do the same with the old starter, as its probably good yet.