This is our 4th day with our 07 3400rl unit. Picked it up in Colo and am now in Central Oregon. Pulls well with our dodge 3500. Only problem thus far is that the landing jacks do not operate. I unhooked once in Utah and today when we arrived they did not work. Anyone else have such a problem. Beyond that one small detail we do like the unit.
As John said there is a fuse in line in the front compartment, could be a 30 or 40 amp. Trace the leads back from the motor and you should find it. Also check to make sure that all the connections are tight.
On your 3400 the fuse is on the right side front compartment and it is a 40 amp. You will have a very hard time finding these fuses out on the market. I picked up a few at a car stereo installation place they use them on big Amplfiers. I also tried to use a 30 amp only to have them fail unless I let the fuse cool every few seconds when under a load. hope this helps..........
If it happens not to be the fuse, if they work when connected to 110v then it may be a battery problem. I once had a bad ground on the battery that caused the problem you are having. The ground wire from the battery connected to a screw (screw, not a bolt) into the pan of the front compartment. The screw rusted and the hole enlarged, making contact intermittent. Just a longshot in case the fuse proves to be ok.