I'm kind of at a loss now, sorry.
I've done some online research and here's what I have come up with. There is a central cpu that controls all three gauges, I suppose there could be a problem with that. Also, I've seen some reports of people with an aftermarket stereo not getting everything connected back up after installation and running into some problems with the triple pod gauges.
I do have a couple of other questions though...
Was your car running when you took that pic? I ask because one of the tests I tell people to try when they're worried about their oil pressure gauge going bad is to turn the car so that the gauges are on but the engine isn't running, if the oil pressure gauge goes anywhere there's a problem since there should be zero oil pressure. Also, your voltmeter reading is well below normal (if the car is running, if it's off it looks normal) , this is normally the sign of either a bad battery or a failing (failed) alternator.
Both of these issues could very well be related to the other gauge issue, whatever it may be, but I wanted to make sure you were aware of both potential issues.