Look first at the wiring diagrams to find the connector number for the diagnostic plug, if any. Then go to the wiring harness diagrams, which show where the connector is on the harness in the car. Then go digging there, armed with the wire colors and connector type and configuration from the wiring diagram.

This will finally tell you there is no diagnostic plug for a reset. The light is triggered by a rev counter running off the pulse generator in the speedo housing. I think it triggers every 75k miles. There's a reset switch on the back of the instrument cluster, two position slide switch. Impossible to spot from above, look thru the windshield, and it takes a narrow blade tool to get into the switch recess. To remove the whole cluster, remove the rear cover by pulling straight up off the clips. Two big screws hold the cluster in, IIRC. Unhook the speedo cable, disconnect the cluster connectors, and lift out. Waste of time, dig for the switch in place. Bent coathanger wire makes a good switch tool...

The light comes on at 75k intervals to tell you to service the egr system, and you remove the bulb on the third time because who cares if it works, under the then existing reg...