Gene said what I was going to say, so there are 2 of us with the same starting place.
Check what Gene stated and also check for voltage at the breaker for that circuit that something is leaving the breaker. You have to sort out which 15 amp one it is. Process of elimination of what is working verse not working with the flipping of the breakers will do it.
As far as a wiring diagram, we only have 1, it is for my prior 2004 T2499. While it is for that year/floor plan, it fits some of the newer campers in the way Sunline split up the loads. This is in the files tab at the top of the forum. When logged in, click the words "FILES" and a bunch of good stuff is in there.
Your "General Purpose" 15 amp breaker is most likely feeding the circuit you are after. The bath GFI might not go back direct to the breaker. It might tie in on another receptacle and then jump to the GFI and other wet areas. That wiring string is year/floor plan specific. My 2004 T2499 picked up the bath GFI power off the fridge outlet. Then left the GFI and went to the outside outlet. Yours may differ.
And check that the new GFI is not accidentally mixed up with line and load. It is a common mistake. Even the white neutrals have to be on the correct side of the receptacle.
Hope this helps and report back what you find or need more helps
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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