hi installed new header got check engine light would a obd1 or 2 conversion harness help. (1990 accord), did search but no solution for the problem thanks.

 

u need to see what codes the ecu is throwing. most likely u didnt hook the o2 sensor back up.

 

code 41 and 12

 

I wouldn't bother converting to OBD1 as it's not necessarily going to solve your problems... First off, I'm just going off the top of my head but I'm pretty sure your 12 is for your EGR valve... Check into the wiring and the actual unit... As for the 41 that's an primary oxygen sensor heater (PO2SHT) code... You say your car is a '90? You shouldn't have that code as your oxygen sensors don't have heating elements (maybe I'm wrong, I don't deal with Accords that often but it's still nonOBD)... If you have an extra oxygen sensor try swapping it, if the code goes away then you're set... If not then I would trace the O2 wire all the way back to the ECU... Continuity test for break, etc. with a DMM... Just my $0.02