I have a 1990 Camaro RS TBI 5.0 and I'm currently building a 383 TPI engine to swap in I was wondering if I'll have any problems with buying a Painless wiring harness for a TPI setup for a 1990 to 1992 will this harness work with everything in my Dash or will I have to do more work instead of just plugging it in to the original harness in the dash

 

With the stand alone harness you will need to wire up the speedometer from the ecm as well as the check engine light.
You might consider reworking your tbi Harness
https://www.thirdgen.org/forums/tpi/...d-density.html

 

It sounds like it might be easier to find a used TPI harness

 

I repined the existing TBI 746 ECM wiring harness to match a TPI 730 ECM on my 1992 Firebird convertible when i did a 305 to 383 swap.
Repining is not that difficult. A factory service manual for your car will help immensely as it will have the wiring diagrams and pin outs needed.
Pins, pin removal and crimp tools, and new connectors are available online.
Third Gen forums are a big help - just need to do a little research to find what you need.
I added dual fans and had to add wiring but again a factory service manual was a big help.

Good Luck