How do you test an oil pressure sender?
First you need to identify the oil senders type. First read about what an oil sender does and how it works and other generator protection devices. Make sure its an oil sender and not another type of oil pressure sensor, like an oil pressure switch. Once you have determined you have a oil pressure sender you need to find out the type. You need to know the type of output you should expect and also how the different resistances or voltages relate to oil pressure readings.
Your supplier might show you the curve, in this example here is the curve for a Murphy 7 Bar and a VDO 10 bar sender. Here is a Murphy oil pressure sender, part number 00-00-3029
As you can see these are both totally different and as such you need to make sure you know which sender you have or you won't be able to check if you are measuring it correctly.
In this instance you can see the resistance of the oil pressure sender and how it should change. Before testing this, you will want to disconnect the oil pressure sender from the generator control module, as leaving it connected can give you unexpected and incorrect readings. Using a multimeter you can measure the resistance of the oil pressure sender as the engine is at rest and see if it matches the reading supplied by your manufacturer.
In each case you may want to run the engine to determine if the switch is changing state. Before you do this you should try and prove that the engine doesn't have an oil pressure fault, by fitting another sender that works, for example, or reading the engine oil pressure from a secondary device, such as an oil pressure switch, which may give an alternate readout on your generator control module. You could try the sender on an engine you know has oil pressure. You should not in any circumstances run an engine where you are not 100% confident that the oil pressure is at the correct level, this may seriously damage the engine by causing catastrophic failure and may lead to injury or death.
Once tested if you think the oil pressure sender is OK - see what else could cause low oil pressure.