this ignition harness is for 73-74 as it does not have the connection for the fan at the end of the harness. this wire is something modified by a PO (swap meet harness) so the wire is NOT in the Haynes
and is not stock/factory and does not run the heater fan, it is a tap off of the pin 11 to power ..... something. i was just thinking that someone might remember modding a harness for carbs or a connection for key on fuel pump for example and telling what this is for. i'm going to return the harness to as stock a condition as i can and reconnect the jumper wire between pins 11 and 12.