how would the computer know that its not on its original home?
One of the problems is that the load (ohms) in the original harness is pre-set into the box (not a variable input from a sensor), as is the range of battery voltage and alternator/regulator output. There is also inductance in some vehicles from big stereos, ABS, etc.
I don't know any way to match this when wiring up an older vehicle since some of them are variable. Most work very well, but the odd exception (including non year-correct factory parts in an original EFI car, aftermarket lamps, big stereo, alarm added) makes you wish carbs were back.
