Amp protection light

I have one JL Audio 500wx4 and one JL Audio 350wx2. The 500 is for my tower speakers and the 350 is for one 12"L5. Both ams have their own Pwr and Grnd wires but the rem wire for the 350 runs off of the 500, and they share the same batt. When the radio comes on the 500 turns on with no problem but the 350 shows a protection light. I have swapped out the the 350 and tried two other amps with the same result. Any ideas would be helpful.

Either the sub or the sub's wires are shorted. Disconnect the sub at the amp and see if it powers up right, then check the sub and wires with a DVOM for low impedance (short)