charging problem

[89CobraGT]

I recently rewired my alternator wiring for a the 3g but i actually only have 100 amp and ever since I did this my charge is like 12.9 volts constantly while the cars cold, I can have the heat on and stereo up and it doesnt move but as soon as I get to operating temps the voltage drops and then it was going back up every once in a while but today it was 37 degress C and I drove my car for maybe 20 mins and it died v_v I dont know why it matters when the cars warmed up it doesnt make any sense to me. I checked my wiring today too and it looks fine. if you have any advice I would appreciate it

 

[89CobraGT]

I recently rewired my alternator wiring for a the 3g but i actually only have 100 amp and ever since I did this my charge is like 12.9 volts constantly while the cars cold, I can have the heat on and stereo up and it doesnt move but as soon as I get to operating temps the voltage drops and then it was going back up every once in a while but today it was 37 degress C and I drove my car for maybe 20 mins and it died v_v I dont know why it matters when the cars warmed up it doesnt make any sense to me. I checked my wiring today too and it looks fine. if you have any advice I would appreciate it

I forgot to mention it drops to like 2volts when it gets hott with no stereo on or anything else I just finshed checking my wiring and grounds and everything seemes to be ok the battery is a dry cell odyssey just bought last year and the alt is a 100amp jegs also bought last year