Here is a photo of the obd connector on a 1993 Isuzu Trooper.
The connector is on the transmission hump about 6 inches from the accelerator pedal. It is inside a black hood. Right next to the white OBD connector is an identical green connector that I have not tested.
The OBD port is a white 3 hole plug. Right next to it in the photo is a green 3 hole plug that I believe is for automatic transmission diagnostics. The plug is different from other plugs under the dash as it will not accept a .25" tab connector.
The picture shows a 20 ohm resistor being used to short pin 1 and 3 of the white plug. The resistor is to prevent a melted wire in case the plug shorted is the wrong plug.
To read the error codes from the engine computer, the mechanic is supposed to short pin 1 and pin 3 of the OBD port plug. Then the mechanic turns on the ignition switch and counts flashes of the "check engine" light to determine the error values being reported.
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