Will a wiring harness off an
04 type s work with a 03 si motor an ecu? Or could I use the ecu out of the type s on the si motor?

 

you can't use the Type-S ECU because the engines are ran completely different and internals are completely different.

As for the harness I'm not a huge EP3 guy but I believe you can but don't quote me on that one

 

yes the harness will work

 

Thanx guyd