I would humbly suggest that next time, don't take the return spring off the foot stomper linkage.
Listen, the foot-stomper was designed to be mashed or stomped with yer boot. Now, if ya cain't reach the foot stomper with yer own boot, 'cause yer gonna be workin' with yer head under the hood, get some cowboy to he'p ya. 'Bout anybody I know would be more'n happy to drop by, set in the cab, 'n' mash the foot stomper whenever you say so.
Now see, when you manually actuate the linkage with a screwdriver sans return spring, you do run the risk of having a continuous electrical connection with that starter switch on the top of the starter motor housing.
That might explain the shorted (sic) positive cable. I really don't think you have anything "shorted," because a short involving the positive battery cable results in things getting red hot real quick, burning insulation, and a release of all smoke contained in the cable and maybe the battery to the real shouting event called "fire!"
I suspect that when you engaged the starter with the lever (screwdriver) instead of your foot, with the return spring on the mechanical linkage disconnected, the whole starter motor remained engaged electrically, since there was no reason (such as the return spring) to return to rest.
The overrunning clutch inside the starter motor presumes that once the engine begins to run faster than the starter motor that you will take your foot off the stomper. The spring on the linkage pulls the linkage away from the actuaing lever and the electrical switch. The overrunning clutch drops the pinion gear out of the flywheel and everything goes to rest inside the starter motor until you need to start the eingine again.
Uh, oh! One BIG thing you mentioned. 12 volts vx. 6 volts. Oh, horsefeathers! Get somebody else here to chime in on 6v vs. 12v. vs. number of flywheel teeth, vs. chew your starter and/or flywheel all to heck and spit the parts out.
Quick! Go read some Tech Tips!!!!!!!
Do it before you reinstall the starter motor and try once again to fire 'er up!
