car wont start

[savethes13s]

i just finished up my girlfriends swap this week. when i was done i went inside to fire her up, everything was fine, all except a rough idle. the swap that was performed was a 13 twin to a 14 twin (96 model). her car is a 1993 s13 coupe. after doing all the usual maintinance to the engine , i let it rest for the weekend. came back to work monday to do the final touch ups, now it wont start. the funny thing is now the rpm gauge dances when i turn the key in the on position and proceed to start it. i can her the starter clicking trying to engage but no action.what could have caused this reaction. i've went through all four of the transmisson sensors and no cuts. the battery that i was using was pretty drained but can this contribute to the rpm flutter? any suggestions well be appreciated. also i heard that when you do this swap one of the units you may have to swap out is the throttle body for the 13 unit. could this have contributed to the rough idle?

[himajinga]

Yes, my car did the same thing. Your tach jumps around and you hear a click? You've got voltage but no amps. Newer battery should solve it.