There is an in-line fuse close to the battery terminal or maybe just under the front frame. Mine was a 30AMP I believe. Look for that...
You say you are getting 12.5VDC at the battery terminal. Sometimes the terminal is corroded so test at wires feeding the battery not in the center post.
Also can you find the RED wire coming from the battery at the converter. With the converter unplugged from shore power test that for the 12.5VDC you are reading at the battery. Must be a disconnect somewhere in this leg between the converter red wire and the battery terminal.
Are you sure you don't have a BATTERY DISCONNECT switch installed close to the battery???
Since you have the multimeter this should not be a real hard thing to figure out where you are losing the 12.5VDC.
My POPUP trailer also has a fold-over cabinet switch that disables alot of things including the ceiling lights if the sink/stove cabinet is folded over for travel mode. There should be a plunger type switch on the bottom cabinet that gets pushed in when you setup the sink/stove part of the fold up cabinet. Check for that not being pushed...
If you accidently hooked up the battery cables in reverse and they just sparked once it will blow the in-line 30AMP fuse I was describing above as well as a 12VDC fuse in ELIXIR fuse slot. The manual calls this fuse the REV POLARITY fuse or something like that. Before I changed out my old ELIXIR for a smart mode converter it had four plug-in 12VDC fuse. the first three was for three 12VDC circuits, the forth one was the REV POLARITY fuse...
There is not a whole lot involved here between the converter and the battery connections. Start at the battery and read your 12.5VDC then follow the battery cable and try to keep reading the 12.5VDC at junction points until you get to the converter.
My Starcraft unit had a whole bunch of those YELLOW twist connectors along the way back to converter. One of them may be a bad connection along the way.
My Posts are IMHO based on my experiences - Words in CAPS does not mean I am shouting Roy - Carolyn
RETIRED DOAF/DON/DOD/CONTR RADIO TECH (42yrs)
K9PHT (Since 1957) 146.52M
2010 F150, 5.4,3:73 Gears,SCab
2008 Starcraft 14RT EU2000i GEN
2005 Flagstaff 8528RESS
I was just rereading things - I noticed you definitely checked the REV POLARITY fuse that is on the ELIXIR unit. Also check for an IN-LINE fuse closer to the BATTERY install. Mine is located under the front trailer frame close to where the electricl box with lid is for the 7-way cable connections. Looks like this:
Photo from google images
Mine has a 30AMP ATC blade fuse in it...
You should be able to determine if you have continuity between the battery terminal and the ELIXIR unit using you multimeter. If it reads 12.5VDC on the battery side with the trailer unplugged from shore power it should also read 12.5VDC at the ELIXIR location.
This shouldn't be this hard to determine. Maybe I am missing something haha...