Before I begin, let me advise of an insulation color change for "12v" electric wires between your 2009 TM (older USA standard colors) and your somewhat newer electric tongue jack (newer international standard colors):
In TM "12 Volt DC" wiring, the +12V wires are BLACK, the negative return wires are generally WHITE. In newer equipment, and especially in devices from China, the +12V wires are RED and the negative return wires are BLACK.
In all cases, +12V wires should be fused, and grounding wires should never be fused.
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Your Electric tongue jack BLACK wire is bolted directly to the the "-" post of the battery. That post also connects a slightly larger WHITE wire (AWG-8) marked "Neg". The other end of that wire is bolted into the TM frame. Even though the conflicting colors look weird, this is correct. If the bolt connection into the frame is good and tight, then the grounding side of "12v" to the TM lights and other loads is good.
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Your electric tongue jack RED is bolted directly to the "+" post of the battery. If the tongue jack does
not contain a replaceable fuse,
then a fuse should be added along this wire. I SWAG the correct size to be 30A or less, because the insulated wire (and its matching black "negative return" wire) seem to be no larger than 10-AWG.
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Your most likely current issue (the +12V wire path to/from the TM "load center" 12v circuit board) might occur in 3 places:
- the funky inside side-mounted battery fuse (it's probably probably a big one).
- the long wire from that fuse back to the TM loasd center fuse board.
- the smaller ATC fuse supporting that fuse board connection (within the load center).
I don't like that fuse mount, located partway down a narrow side of your fuse box. You can't readily see if the fuse (or breaker) has blown until after you have disconnected the top mount wires and removed the battery. The current wire size from the battery mount is very large, and the fuse must be limited to the smaller wire coming out. (It's probably way to big).
The standard "+12v" wire between the front-mounted batteries and the WFCO circuit board connector is only 10-AWG, and the supporting fuses must not be larger than "30A". If you want to support more than "30A" between the batteries and the rest of the TM (including the power converter main board), then you must upgrade that entire wire to AWG-8 or larger, depending on maximum load which want to allow.
The fuses (WFCO 12v board, size "standard ATC" maybe upgraded to 40A for the case of 8-AWG wire. At the battery, under the top cover, I recommend use of a "maxi" ATC fuse instead of the smaller-legged "standard" types. Fuse holders for the "standard" ones are generally provided with 10-AWG maximum pigtail size anyway, which is not adequate for the larger fuses people sometimes install in error.) Here's a two-pack, you'll need to buy the 40A "maxi" fuses separately (Buy more than one, to have spares.)
https://www.amazon.com/VANSIHO-Water...dp/B0B6R8J932/
If you choose to undertake the wire upgrade, I recommend that you change from TM's 'BLACK' insulation color, and buy RD wire instead.