Not trying to get into a debate here, so please,,don't take it that way,,
It's very sad that this happened, obviously, but why it did is also important for other's.
CM and DB are actually both right in a sense,
the solenoid on the starter has two bolts with nuts (actually 3) if these two bolts are shorted together,
*** A typical starter solenoid consists of an electromagnet coil, with a sliding armature. One end of the coil is internally connected to ground (the case of the solenoid, while the other is connected to a small external terminal . . . when positive voltage is applied to this terminal, current flows through the coil and pulls in the armature against a return spring. The distal end of the armature is connected to a conductive (typically heavy copper) bar that bridges (shorts) the two heavy contacts (the larger terminals on the exterior of the solenoid - sometimes also called a "contactor"). Note that the two heavy duty terminals are normally open. Installed on the tractor, one of these terminals will go to the starter motor positive terminal, while the other is usually wired directly to the positive terminal of the battery. These terminals will often have rubber insulation covers to prevent inadvertent shorting to ground.
Shorting the battery connected terminal to ground (as with a wrench) would cause prodigious amounts of current flow, arcing, sparks, welding etc. Shorting the other, starter motor connected terminal to ground (as with a wrench) would do absolutely nothing. Shorting these two heavy duty terminals together will typically cause a small arc (sparking) and power the starter motor.
In Gary's situation, his wrench most likely bridged or shorted (connected) these two heavy terminals together (ground was not involved at all) - period. ^^^
they will turn the starter, once you let go of these with your wrench, the starter will stop.
These two bolts are "positive charges" not negative in any way, *** Correct, however as explained above, one terminal is positive, connected to the battery and until the solenoid is energized, the other terminal is simply "open" no voltage (though if you were to check resistance with an ohm meter, you would read resistance through the starter motor windings to ground). ^^^
bridging these two bolt, will "bridge" a positive feed to the starter, *** Correct, bridging or shorting together these two terminals will energize the starter motor ^^^
BUT...
if you "accidentally" GROUND your wrench while doing this, (as in touching the starter casing),
you have now "shorted" out the solenoid, keeping a constant "bridge" between these two positive terminals, hence the continuous turning of the engine. *** No, not exactly correct - bridging the two bolts will energize the starter, TRUE. IF, while doing this, the metal wrench is allowed come into contact with tractor ground, serious arcing and current will flow to ground through the likely very hot wrench - the wrench and terminal will be MELTING! at their contact points, held grounded long enough (assuming one is wearing asbestos gloves or the wrench is now jammed in position, can also melt the battery cable, ignite its insulation, or cause the battery to explode. ^^^
This is why it's very important when starting the starter in this manner, that the wrench does not ground or touch any ground source.
*** Absolutely! In Gary's accident, his wrench was likely bridging (shorting) the two heavy contacts, causing the tractor to suddenly lurch forward. As it did so, its movement broke the connection between these contacts and the wrench, momentarily de-energizing the starter and stopping the tractor. However the pressure on the wrench from his grip caused the connection to remake, moving the tractor again, . . . repeat. Note that "grounding" these terminals did not happen in this sequence. Semantics? No . . . "shorting to ground" was not involved in this process and would not energize the starter. ^^^
Also, neither CM or DB are on my ignore list,
I believe everyone here has valuable knowledge to share, whether positive or negative.
