Fuel pump is on back right hand side of the unit. 110VAC voltage regulator, 110VAC circuit breaker and 110VAC wiring connections are on front right side of the unit. If you did not drop the unit (or if it is not on a slide out), then you had to reach past all the 110VAC components/connections to acces the fuel pump. You may have jostled something loose.
Installation Manual: http://www.cumminsonan.com/www/pdf/manuals/965-0631.pdf
Refer to pdf page 8 for location of components. Speciffically the Voltage regulator and 110VAC conduit routing. Check for loose conncetions. Cycle the 110VAC circuit breaker on side of control box to make sure it is working properly.
Service Manual: http://www.cumminsonan.com/www/pdf/m.../965-0531B.pdf
Electrical wiring diagram on pdf page 132 (B-5). Not much to this. Field voltage applied to Voltage Regulator (VR1; P4). It supplies voltage to TB-1 which is routed to CB-1 (You only have a single 120VAC output based on the FA designation in model number). 12VDC field excitation comes via pin 7 on VR1 from the A1 board assembly during start up (Explained in Section 8 - generator). You have a SPEC F generator so you have the pre Spec G electronic governor.
Initial thing to check is wiring connections.
Do you have an Automatic Transfer Switch (ATS) or do you manually move a a plug to switch from shore power to generator power. That era of rig could also use manual circuit breaker switching. If ATS, the detection circuit could be failing or the connections could be corroding. Manual circuit breaker switch could be a bad breaker. Plug style could be a failing blade or connector. You will have to just work through potential problems using a voltmeter to locate where the 110VAC is dropping out. See if you have 110VAC at the CB on the generator first (both sides of breaker). Then work from there.