Failure at the transmitter / receiver

Have 3 pieces heir of Ordered only one of which works perfectly, the other two seem to have problems. To have the power supply.
We have 3 horse trailer equipped with it in order to watch the horses while driving.

In all 3 trailers in the trailer the identical lamp is installed. Be of the lamp, we have taken in a current of all followers dad works perfectly with the other 2 sorry to the bulb of the lamp taken out otherwise just a gray spot appears on the screen. Despite the same car and the same lamps kammera ..
However, who is out the bulb. If it works wonderfully.

Another unpleasant feature is the extremely thin cable of the radio transmitter which you should very careful when handling