I have an aftermarket head unit out to an after market single channel amp out to the factory sub. the amp will not play wired in series or parallel. both voice coils will play if connected individually. both voice coils ohm 2.1

 

what is the rating on your amp. its a dual 2 so a 1 ohm stable amp is possible but not common (wired in parallel) which leaves basically just series as the only viable option. maybe double check your wiring that its being done properly? the stock amp had individual channels for each coil but that shouldn't matter (in theory idk in all reality)

 

Nice to see you still around as well

 

amp is 300W at 4ohm, 400 at 2ohm. no spec for 1 ohm but says 1 to 4 ohm stable on the amp. plays fine when connected to a different sub speaker. guess my options are to run one voice coil, replace the speaker or find a 2 channel amp.

 

300 RMS is more than enough for that sub. it really cant handle much power so series should work for you. since you said it wasnt working in series either sub could be wired wrong or hooked up to the amp wrong or amp could be busted somehow. slight possibility of a power or ground issue but if it plays on one coil thats likely not going to be it