can i use a 1990 4runner engine harness in a 1989 4runner.both of them are 4cylinder 5 speed.

 

Maybe. The problem is that there is no single standard harness for the yotas even on the same model and year. The harnesses varied depending on what options were present on the truck.

The big problem is that every model year had variations in the emission control stuff which in turn meant that the wiring harnesses were different.

You might be able to use the harness from a '90 with some modifications.

 

The EFI should have both been the later "straight" throttle body intake.

But there were California variances etc... so it might have some things that dont match up fully...