Putting a 06 Chevy 1500 pickup 4.3l v6 vortec engine in my 94 s10 Blazer Tahoe LT 4 wheel drive! Want to know if the wiring harness is interchangeable and the connectors and sensors will hook up? I have the old motor as well both motors have the spider injection system

 

The harness will not be interchangeable. I'm not even sure the block is 100% interchangeable, as I think they use different knock sensors, and the 06 may not have an EGR. The 2002-2005 S-series trucks with the 4.3L do not have an EGR.

Your best bet would be to use a donor block from a similar year of truck. If you are going to use the 06 engine, you should use all the original sensors and harness from the 94 on the bare 06 donor block.