No 12 volt at the panel

Figured it out. When Keystone built my Cougar they sandwiched my 12 volt line between the frame and floor. Causing the intermittent short. Had to take it to a repair shop to figure it out. $400 to get it fixed, but the repair guy took a bunch of pictures, and I sent off a letter to Keystone and they reimbursed me for the entire repair. No questions asked.

I will second that test light.. I have had a couple of problems (one this week) where a volt meter alone showed or would have shown "GOOD" but the test light was not at all bright.

Test light draws 1/2 to 2 amps depending on the light,, Voltmeter about 1mA (1 1/000th of an amp) OR LESS depending on the meter and the problem was a wire that had gone high resistance in both cases I quickly found and excised the bad section of wire.

Multimeters are ok but may show a false voltage reading with no current if a circuit has a high resistance. (To prove this take one side of the multimeter to one of the battery posts and the other to the battery case. You will read voltage which will rise the closer you slide the test lead toward the other post) A test light is much better in troubleshooting the 12 volt supply.

X2 BFL a Multimeter is your friend find where you have power and follow it to where you don't, the trouble is in between. If you do not know how to use one, learn they will find 90% of electrical problems, a good tutorial http://mechatronics.mech.northwestern.edu/design_ref/tools/multimeter.html

If you are not plugged into shore power or gen, you are on battery.

If on shore power and converter is not working (various reasons) you will still have 12v from battery--unless:

-Battery disconnect switch is open
-Battery fuse or circuit breaker is open (as mentioned above)
-Some other open somewhere battery to panel

If just on battery no shore power and no 12v to panel--same three as above.

There's usually an auto-resetting breaker either near the tongue or near the panel or even both. The breaker(s) could be of the manual reset variety as well.
Then there's also the reverse polarity fuses at the converter panel.

Happy hunting!
Scott