So i just installed a tach cluster into my car and when i hit around 3500 rpms or so my oil light goes off and it buzzes. Ive never had this issue not to mention both of my oil pressure senders are disconnected.
If both oil pressure sensors are disconnected, that would be why you are having the issue. The sensor at the oil filter is closed when there is pressure, open when there is no or low pressure. So if the wire is disconnected, you are telling the dynamic oil pressure warning system that there is a problem.
If you really do not want to have the warning system (I'm assuming you have another oil pressure gauge or something), you can ground out the wire that would be connected to the switch on the oil filter housing. Leave the one at the head disconnected though - that switch works the opposite way.
If you didn't have this issue with the old cluster, it's probably an issue with the new cluster as the oil buzzer is known to have issues. It's easy to swap out. You'll have to search around for how to as it's been quite a while since I did one.
However, you would be very wise to verify your pressure with a gauge to make sure that it is in fact ok.