i have 440 in 74 cuda with a march proformance one wire altenator that has a built in regulator i also have a msd 6al. when i hook up my altenator i run one wire straight to my battery eliminating the big black wire that went from my stock alt to my bulkhead. what sort of problems am i going to be encountering? im not to experienced just learning from trial and error any info grealty appreciated!

If you eliminate the large black wire the ammeter won't work, current needs to flow in both directions to show charge/discharge on the ammeter and eliminating the black wire will only allow the ammeter to show discharge.

so what should i do with the big black wire? where should i hook it

If you want the ammeter to work you have to hook it to the alternator lug.

with a wire directly from the alt to the batt the ammeter will read but not correct. I'd suggest an 8ga wire between batt/alt w a 12ga fusible link to protect that line and connect the 2 large wires on the ammeter together on one stud of the ammeter & add a voltmeter via switched 12V though I too am old school & I like my ammeter (& an added voltmeter also)