1) Check your fuses.
2) If fuse is ok, remove the amplifier from the wall and test for 12 volts at the back of it.
3) Check the ground wire with an ohmmeter to trailer skin.
4) If 12v
is present and ohmmeter shows continuity, amp is probably bad.
I have a stock one which I removed when I upgraded to one that shows signal strength. If I can find it, you're welcome to it.