Car: 1993 400SEL
Engine Harness Part #: 1405401132

The MPG gauge seems to be working fine and showing the correct reading except for what I describe below:

Before replacing harness : (also coincides with the owners manual)
Car @ idle – maximum reading
Car Off – zero reading

After replacing the engine wire harness:
Car @ Idle – zero reading
Car Off – maximum reading

It seems that the MPG gauge is behaving rather the opposite of the norm. I know logic says that reading should be "0" at idle but this is backwards of what i had before the wire harness.

I have the correct engine harness. I checked all the connectors and verified all seated correctly. Most of the connectors are “keyed” except for the couple of connectors in front of the engine (coolant temp and the one immediately to the right of it). I checked both to be correctly plugged in.

Just asking for any suggestion what’s causing this behavior and what to look for next.

Thanks for all your help.
Chedeng