If I'm reading the service manual correctly the oil pressure relief is only accessible after splitting the case halves. somebody please tell me there is an easier way. I'm trying to solve a low oil pressure problem in a freshly rebuilt engine and would prefer not to pull the motor apart again.

usually problems with the oil pressure relief valve would lead to high oil pressure.
As the engine was freshly rebuilt I wonder if there`s air in the oil pump and it lost its prime. In that case you could try to remove the upper plug on the front right of the engine (the one above the oil pressure switch, where on other Ducs the exit hose to the oil cooler is attached) and pour in some oil there. Then wait and try again.

Excessive oil would have to be removed again however trying that would be easier than splitting the engine.

does it matter which hole the sender is in? I've noticed that the service manual shows the sending unit in the lower hole yet some other resources and pics show it in the upper. mine has had it in the upper hole since I bought the bike a few years ago.

the parts catalogue also shows it in the lower hole.
If it makes a difference I don`t know specially if both holes are above oil level.
Maybe someone else here knows?

Weirdly I experienced this exact problem today.
I fired up the 907 after the winter lay up and service and the oil light stayed on. So I removed the oil pressure switch, it's in the top hole on my bike, and with an oil can squirted oil in until it filled up. I refitted the oil pressure switch and fired the bike up. The light went out instantly
In my many years of Ducati owning I have heard of this air lock problem but this is the first time I've experienced it.

Derek, out of curiosity. The oil pump is on the right engine side. Did you have the bike parked on its side stand over the winter? Just wondering if that could cause air getting into the oil pump.

No, I parked it on the centre stand but after draining the oil I left it for a couple of months before refilling. This may have allowed the pump to drain and hence the subsequent air lock. I didn't change the filter because it had only done about 1,500 miles last year.

You can get the relief valve out without splitting the casings. Remove the alternator cover and beside the gear shift shaft there is a brass looking plug remove it and you can get the valve out