When doing a 305 to 350 swap do I need to change the harness im using a goodwrench motor

 

By the way guys its an 88 trans am if that helps

 

Unless your changing induction system to something other that what the 305 is the harness will work.

 

Im going from fuel injected to carb

 

You can modify your harness or sell it and strip down one from the junk yard. You need switched ignition to your distributor, alternator, ignition switch to starter solenoid, you didnt state if you have a automatic for tcc lockup or manual trans. Depending if this was tbi or tpi rewire for a manual fan switch or better install a single wire grounding coolant temperature switch to control the fan. Do a search there is a thread on converting from if to carb.