In order to reach the negative terminal to the battery in a 2000 Vebture (I have one) you must first remove the fuse housing. The fuse housing is a large black box that sits atop the battery. There os a single bolt that holds it in place located in fron of the battery bolted into the lip of the motor bay. Unscrew this, then unhook the fuse housing from the cross bar running from the back roght to the front of the motor bay. This is a tight fit so watch your knuckles. Once the fuse housing is out, the negative terminal is located on the backside of the battery. It is a tight squeeze black is negative, red is positive.
The button is not working. It's programmed if the other functions (buttons) work. What you can do is take it apart, clean the rubber part (the buttons) with soap and warm water. Then, use a cotton swab and rubbing alcohol to clean the circuit board where the back of the buttons contact the board.
Without testing we'd only be guessing , your best bet ,take it to a qualified repair shop that has the diagnostic skill's an testing equipment . Hooking up a professional scanner . 016 Engine Misfire Misfire Scan Data
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If you think the problem is a fuse or circuit breaker, I see three fuses and a circuit breaker. Use a test lite and check voltage at circuit breaker and fuses, some are hot all the time, I believe one goes hot with the key on.
the first thing to do is to have the oil pressure read using a mechanical gauge
that ensures that you know that the engine is running with the right oil pressure
you can test the ECM operation by using a substitute ECM that is a known good unit
run the fault codes to see in the oil pressure sensor is a problem
At this point , test the oil pressure as suggested then change the oil pressure sensor
My guess is a fuse in the fuse panel at the far passenger side of the dash,you have to open the passenger door to check it or ....is the interior light over ride switch above the rear view mirror in the correct position for interior lighting?