Starter wouldnt crank when shorted too battery new one does the same

[SIXTYFOURGHIA]

My trusty 64 ghia daily driver(converted to 12v) ive driven daily for 5 years wont crank over or crank with a jump from another car?, i bumpstarted it home and tested voltage from battery to ign switch all getting 12+v, but the headlights dont work also without car running? theres 12v out of the headlight switch too the fusebox. i jumped with a remote starter from the battery too starter and still nothing, i get a medium spark when jumping the main power and solenoid on the starter with a screwdriver but no cranking, so got a new starter and it does the same, im showing 12v at battery and starter terminal. the battery power comes through the headlight switch, can it be something in the headlight switch? i ckecked the ground at the motor with a voltmeter and was good, the transmission ground is solid but i havent tried grounding it with jumper cables or tested it yet at the strap. When the starter wouldnt crank with direct battey voltage i assumed it was the starter so got a new one and it does exatcly the same? could the headlight switch or ground be causing this? what am i missing? Thanks for any help or suggestions.

[Dale M.]

Have battery tested.... Just because it shows 12 volt does not mean it does not have dead cell (S).... If you are jumping from another battery or jump box the circuit that powers starter is very small... Positive side of battery to starter solenoid, negative side of battery to chassis and then ground strap around transaxle mount.... IF battery tests good, you have poor connection in circuit some place ... If you short terminal 50 on solenoid to direct 12 volts it eliminates all other wiring in car, and if it still does not work you have eliminated most of cars wiring...

[sideshow]

If you can bump start...but not key start that is usually a bad ignition switch.
Also that style of ignition (headlights off w/engine off) is not normal behavior for that era.

And screw driver cranking (while nose is supported) is very traditional test...if that doesn't work I agree with/D

[SIXTYFOURGHIA]

Thanks Dale and sideshow, spot on! it was a dead cell in the battery i blew it not testing under a load. thanks again!