| MOST ECU type of 'Outputs' are taken to ground.. ' One Load wire' ( either heater, or sol coil ) will be tied to a fuse to +12 Batt.. the other end of the 'Load Wire' will go to a wire at the ECU, where the ECU will ground it when requested.. In Computer terms it's called a Sinking Output.. the ECU will Sink the power to ground.. to get it to turn on.. If you have the ECU Unplugged at the Connector Harness, the Red/Brown wire will not be grounded.. it is driven through a relay to +12 hot.. The Red/Brown side of the 'Load' will always be hot when the key is on.. The 'Other than Red/Brown' wire ( like the Green on the AIV or the Slate/Blue on the Wastegate Control ) will be at +12 when the Device is NOT running ( off ), and at about .5 Volt (to ground ) when it is 'On'.. the 12 volts comes through the Coil ( load ) and is not going to ground.. that is why you see +12 Volts on it when it's 'Off'.. The 'Off State' will always be .5 Volts above ground.. as Transistors can not get any closer to ground than that ( OK I'm generalizing here.. don't flame me.. ) GENERALLY ECU designers like to run an 'Open Collector Output' ( Current Sinking) controls on ECU.. they can handle a wide variety of voltage differences and still operate well.. The Fuel Injectors are taken to ground through the ECU.. ( The Injector Coil is tied to HOT ).. but the Ignition Coils require more current than the ECU can handle, so the 'Current Sinking Output' of the ECU drivers is hooked to a Transistor Pack ( PTU ) that actually handles the Power from the Coils. The ECU only handles the Power needs of the PTU Pack.. Cj
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