I want to replace my engine harness....and believe that the appropriate Impala reproduction is pretty much the same...except for the cold /hot light temp sender wires.
I think the biggest difference is the charging circuit. If I remember the Impala has a charge light and the Pontiac has an amp gauge. Someone will probably post more information.
I think I posted a while back about this....charge wiring is different between the Impala and Parisienne due to a light vs gauge situation. There is a resistor wire in the engine bay harness. Also there is an "inboard of the fuse box "difference up to your dash cluster. Mostly it's that resistance wire length that seems to affect things...longer=more type thing. It is a specially wound wire ...for heat and such.. White in color. Mine was burnt due to the wrong coil installed. It melted the harness near the coil/firewall. So I bought an Impala engine bay harness which was less the resistance wire and added a resistance wire along side ie; zap strapped it on I think. Now It works ok but...I put a new sender in my fuel tank and I believe this is also affected by that resister wire following thru the junction block to the cluster.....Yikes....lol. In other words...this wiring is very specific.
also....I will add that 63 was the first year of an alternator over a generator. The harness had diffs there as well. So year over year AND Poncho vs Chev....oh AND Canadian vs American made!
