Hi, I have a GM create motor 350 ci/300 hp with a single rear main seal. Generic engine, I believe it's called Gen III, but not sure.

Currently my 1992 Camaro RS 25th Anniversary Convertible has a 305 E engine with tbi. My question is will my wiring harness fit a tbi from a 350 pickup engine?

That's the $64 thousand dollar question (man I'm dating myself).

 

https://www.thirdgen.org/forums/tbi/...-350-swap.html

 

Hopefully you purchased a Gen-I Small Block Chevrolet Engine... a 350 cubic inch Engine usually is.

A Gen-III Engine swap is much more involved (also requires more Parts) than a Gen-I swap.

Did your new Engine come with an Intake-manifold and TBI Throttle-Body?
...if so, the Engine is definitely a Gen-I Engine, and that will be a much easier swap.

Some of the existing Wiring can be re-used, such as:
-Connections to the Starter Motor Solenoid.
-Ignition-Coil and Distributor.
-Alternator.
-Oil Pressure and Coolant Temp.
-Knock Sensor.
-Electric Cooling Fans.
-Etc.

The Connectors for the TBI Unit may be different... but most other connections will be at the very least similar.

 

Plug and play , just use a 1227747 ecm from
a 87-91 truck automatic or manual whatever your running.
if you don’t have larger injectors from
a 350 you will need those too.