How a starter motor solenoid works 

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This happens because there's 2 moving parts inside the solenoid. One moving part connects terminal 30 to terminal C on the inside of the solenoid. This allows current to go from terminal 30 to terminal C to spin the motor. The second moving part is what moves the pinion gear forward to engage with the flywheel. If the bendix gets too dirty, the dirt and grime can create enough binding/resistance, and the pull in coil and hold in coil don't have enough power to overcome the binding, so the pinion isn't pushed out. This happened on my truck, so I removed the starter, and decided to take it apart. I saw both moving parts of the solenoid were working fine and they had some strength to them. When I tried to move the fork, it would bind, that led me to see how dirty the bendix was. I cleaned it, put on some new grease, put it back on the truck and it worked great. He does show both moving parts in the video at time marker 11:10

The current passing through the pull-in winding in the solenoid switch passes through the field coil and the armature coils before grounding, and this makes the armature to slightly rotate making the pinion to engage to the flywheel ring gear, then as terminal 30 is connected to terminal C, the major rotation starts, during the major rotation, current flow through the pull-in winding stops!

The big battery cable goes to terminal 30, and terminal c connect to the field winding!

@@TheAbJGarage Thank you, may be i am confused with all those C 30 50 sometime called M S D..

@@TheAbJGarage Thank you for saving my life!! Indeed I was inverting terC with ter30. I was concentrating on the solenoid but the solenoid was ok. I was just connecting the wrong way on the STARTER!! Phew, I can go on some other job now! Your video is very instructive. Have a good day.//

It's confusing for me as well because I'm used to calling terminal 30 (B terminal), terminal 50 (S terminal), and terminal C (M terminal).

From what you mentioned, I strongly suspect weak battery is the problem... Have you checked the status of your power supply to the starter? It seems like the battery is not providing sustainable power.

@@TheAbJGarage i test starter on table. And already test battery. Put tester wires on + and - then start starter it only pull so 1.5v from battery. Battery is fine. Today im going to get my new solenoid. Realy hooe then it keep it engage. Now it engage then disengage SLOWLY. And stay disengage

@@TheAbJGarage i also tryed other battery

He's a good teacher and knows that some students need to hear it multiple times in order for it to stick. I know this is a video and people can just replay it, but it may be a habit for him from teaching in a classroom. Everyone learns differently. Some by reading, some by doing, some by watching, and some by listening. My guess is that you're not the listening type...lol. Chill out my man! Life is too short to live all wound up.😀