Barracuda died on lift at exhaust shop.
Yep, to the welding, but likely something simple! Take a deep breath and think some!
NSS is mostly a ground signal to the start relay term G. You may be correct with a poor replacement starter relay. Is it the correct relay stick or auto? We need to confirm some things though.
When attempting to start do you have +12 on yellow at the relay?
Did you try to jump the relay with a screwdriver or such?