Thanks for your suggestions, John In Detroit . I unhooked the lead to the batteries it did not make a difference. The batteries are fully charged hooked everything back up and still has the loud "HUMM". Where does one start in trying to find a short? I don't know much about electricity so I'll need to know what type of meter to use and how.
Trust me, We don't mind answering questions, Heck, we often learn as much as you do from your questions.
You have only done half the test, The other half is disconnect the 12vdc lines from the CONVERTER and see if the noise goes away.... This is also where you start to test for shorth, Here is how.
Unhook batteries, Unhook JUST the positive (normally red) wire from the converter, TURN OFF everything and I mean everything, in the trailer. Plug in converter. If the humm is still there.. Replace converter to quite it down
If you are using flooded wet cells, a Progressive Dynamics Intella-charger with charge wizard is hard to beat
Of course if you are planing on installing an inverter to power your 120Volt toys from the 12 volt batteries. Well, the better ones often have chargers built in. (I kind of like my xantrex)
Now, for the short test, As I said TURN OFF EVERYTHIGN, PULL FUSES if you have to (remember where to put them back please, WRITE it down)
If you have a 12 VOLT drop lamp it's easier but any 12 volt lamp with leads will work, The tubular ones often used for dome lights in cars (with wires on both ends) are often best , with this type of bulb you need two jumpers (Wires with alagator clips on both ends)
Test lamp method, one end of one jumper to one end of the lamp, and one end of the other jumper to the other end of the lamp.... 12 volt drop cord method skip this step
WITH CONVERTER UNPLUGGED!
Hook one lead (either drop cord lead or test lamp lead) to the 12 volt wire disconnected from the converter, Hook the other lead to the converter terminal from which you disconnected the 12 volt lead. Plug in converter
Does lamp light,, IF NO, then no short. Start replacing fuses one at a time.
When lamp lights suspect that circuit, however remove it's fuse and continue replacing untill all fuses have been replaced (Save the ones that lit the lamp)
Now, make sure whatever is down stream from those fuses is truly turned off