7500 Onan Gen won't stay running.

Run the fault code test..
Fault Codes
The genset controller provides extensive diagnostics by causing the status indicator light on the Control Switch to blink in a coded fashion. Following a fault shutdown, the indicator light will repeatedly blink one, two, three or four blinks at a time.
• One blink indicates shutdown due to high engine coolant temperature.
• Two blinks indicates a low oil pressure fault.
• Three blinks indicates a service fault. Press Stop once to cause the
two-digit, second-level fault code to blink. (Pressing Stop again will stop the blinking.)The two-digit code consists of 1, 2, 3, 4 or 5 blinks, a brief pause, and then 1 to 9 blinks. The rst set of blinks represents the tens digit and the second set of blinks the units digit of the fault code number. For example, Fault Code No. 36 appears as: blink-blink-blink—pause—blink-blink-blink-blink-blink-blink— long pause— repeat
• Four blinks indicates that cranking exceeded 30 seconds without the engine starting.
Note: Fault Code Nos. 3 and 4 are rst level faults. Avoid interpreting them as second-level Fault Code Nos. 33 and 44, which have not been assigned as fault codes.

Oki doki, tomorrow I will replace fuel filter and check the 2 fuel lines. Any idea where the oil pressure senor switch might be located and what's it look like? I have the original manual but it's not too much help. I have checked the fault codes when it shuts down. Same as my previous post, I have bought replacement ceiling lights with better manuals.

Locate the oil pressure sensor if equipped. Defective oil pressure switch shuts it down so no damage occurs(if you are lucky). A defective switch or clogged opening will cause shutdown.

Did you check for any rubber fuel lines that may have collapsed?

It sounds like your rig didn't get the best maintenance from the PO.
Check all the lines.

Ok great will do that. But let's say that doesn't do the trick what should I look at next?

Yes, change the fuel filter(s). Always do the simple things first.

Even if it's not the problem, you will know when it was changed for future maintenance.