What is the difference if any at all?? i do not mean between the models, i mean lets take the SI harness from 88 through 91, supposedly i can't use the 91 harness in the 88 and vice versa. Thats according to information i found while searching. But what is the real difference, why can't i use them?
Take the 88 crx si for example what harnesses would work?
Talking about the engine harness here, nothing else......

 

the 88 Si is different from 89-91 Si - it has a square 6 wire connector at the driver's side shock tower, where the 89-91 Si has a round 8 wire connector - the extra 2 wires are for the Fast Idle Control Valve which 88 didn't have

 

is it possible to re-wire/splice it and make the other year harnesses work on the 88?

 

yes, you would need to swap a square 6 wire connector onto the engine harness so that it would plug in or swap a round 8 wire connector onto the 88 chassis harness (using only 6 wires) - the wires that match up are: the 4 injector wires - red, brown, yellow, light blue - the injector resistor box, yellow/black and the EACV, blue/yellow - the ones you don't need, which are for Fast Idle Control Valve are dark blue and black/yellow

 

cool thanks for the info