[mad_b]

Is very hard to compare fuel spent, mainly on a several days/weeks timespan. A bit of change in winds, driver mood and self control, air umidity, air temperature and density, traffic, load in the vehicle and mainly your will to proove the concept may influence the MPG. It is prooved that changing only the way that the driver conducts the car can change results up to 30% yes, thirty percent.
I do agree that maybe your wiring could be rusty and providing a bad electrical contact overall. However improvements to electrical (ignition-sorry I don't know, is your car diesel?) can grant more fuel efficiency, in your case comparing the state of new cables against what was in the car. Maybe just cleaning up the endpoints contacts would yeld the same improvements (even if dilluted among other factors of your economy scenario).