Hey mater4, your question intrigued me as I also have a 1989 345 LE. My manual on page H-66 shows the breaker box (Y-1) right next to the power cord reel & not under galley cabinets. My page H-67 states there is a 6 position rotary switch to select which appliance will receive the 110 volts AC. My MH has neither of these. Maybe AS didn't update all the diagrams with each new years' design.
If only 1 outlet didn't work I'd say check the breaker. If none work there might be a connection problem at the Energenius (univolt). I'm assuming the outlets work on shore power? Does the fridge work on genset & AC? How about the A/C units? If fridge & A/C's work, but not outlets, start looking for power with a tester at the breaker box. check before & after the breakers. PO might have rewired w/o outlets so they could use on 20amp circuit at home (guess). Also check for power at the automatic switchover relay box. It feeds 2 circuits. Maybe you have 1 bad contact there.
Posting these findings may help us diagnose the problem further.
"Sometimes I wonder if the world is being run by smart people who are putting us on, or by imbeciles who really mean it." Mark Twain
AIR 22749 WBCCI 2349 NOVA TAC TN-6
1989 345 LE Classic Motorhome