Transformer was burnt & air handler had a 20amp fuse in place of 3amp. Replaced both with customers approval. Turned system on & noticed 1 wire for the second set of heat strips was left out. Wired it back in & began checking heat. The contactor that was originally wired in began smoking at the 24v coil. The other contactor that I wired in was working just fine. Replaced contactor that began smoking & both heat strips began working just fine. System is heating properly again. No other issues to report.