Starter test question

[Crazyls2]

I have never seen a fly-back diode internal to a solenoid coil, and unless they already grounded one side of it, the solenoid coil is not polarity sensitive. many starters already have one coil lead tied to ground on the starter case and no second terminal to connect to. The second terminal simply allows for more possible control, like a thermal switch or some other interlock in the ground leg.

Now a fly back diode/diodes across that coil might allow us to remove the 100A aux start solenoid on the frame rail and control the starter solenoid directly with K1 as it does not pull all that much current. the large aux start contactor is just the old school way of dealing with the fly-back energy created by the solenoid when you de-energize it and its field collapses...

But where you show to move the ground connection to is how it is shown in the 20-3 manual, starter replacement diagrams...

I don't doubt what you explained, it seems reasonable to me. But, there were no signs of life until I reversed the polarity on those terminals. Once I swapped them the solenoid did it's job

 

[Ronmar]

Same with a relay. A relay is only polarity conscious when it has an installed diode, like is specced on our trucks, so the panel is wired so pin 86 is always + and pin 85 is always ground…

 

[Crazyls2]

I finally got the starter to a shop, it was the solenoid.

 

[MatthewWBailey]

the solenoid coil is not polarity sensitive

I forgot about this thread but saw an update today. I was thinking that plunger rod can get magnetized (weakly) over time, which would be a red herring on a bench top if you reversed the coil polarity, causing it to not activate.

 

[Crazyls2]

Sorry, double post