Dash turn signal and oil pressure light flicker

The oil lamp grounds through the oil sender. Therefore this description does not make sense. I'm not saying "it isn't happening" I'm just saying a common cause is not obvious. The path for the oil lamp is key switch---to dash cluster power at the pin on the PC board---to the oil lamp--through the lamp---to the sender terminal on the PC board connector pin---out the sender wire--out the bulkhead connector---to the oil sender---to ground via the engine block

In theory the voltage to the cluster should not be affected, because the power for the horn relay contacts and coil comes from a different source/ path.

"I don't know"