Speakers went out.
Check that first. If you don't find anything, look for a power distribution block on an amp rack, and there may be fuse enclosures near it. If all that checks out okay, then check for fuses on the amps themselves. They usually are regular colored automotive type fuses near the control switches and trim pots.
If they are using RCA inputs, it's likely they rely on a little "remote" activation wire. If you have a volt meter, make sure the activation wire is charging when the HU is on. Can't remember if it's supposed to be 5 or 12 VDC. The activation signal is likely daisy chained from the first amp on to the next and the last.
Also, which distro block doesn't have a fuse in it? Power or Ground? It's fine if ground doesn't have one, but it should still have a conductor inside or it will be an open circuit.
Can you identify the make/model of the amps and HU?
If they are using RCA inputs, it's likely they rely on a little "remote" activation wire. If you have a volt meter, make sure the activation wire is charging when the HU is on. Can't remember if it's supposed to be 5 or 12 VDC. The activation signal is likely daisy chained from the first amp on to the next and the last.
Most aftermarket amps use a 12V "remote turn-on" wire (blue with white) from the head unit but the use of signal sensing or a remote turn-on wire is not dependent on line-level versus speaker-level input. Either type of input can be used with either type of amplifier activation. A remote turn-on wire is easier and cheaper to implement in an amp's design so it is much more common than signal sensing.
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did you find the 30 amp fuse in the 2100b and check it?
The US Amps document also indicates there is an internal 50A fuse:
http://www.usamps.com/technical/pdf/wp100_99.pdf
http://ampguts.com/forum/us-amps-244...sa-100-a-3491/
You can also try disconnecting the speakers and see if the amps turn on one at a time. Did you ever determine how the amps are activated? Did you verify the remote wire voltage is there?
Try isolating elements and run just one amp at at time with no load (speakers disconnected). People really want to help you here, but we need to know which of things we suggested you have actually tried so far.






