Yes it can be. In can also be levels adjusted too low. Check the inputs to the amp, is there just RCA's? Are they hooked up? Factory radio probably doesn't have RCA outs, so possibly it had an aftermarket radio that the prior owner took out, therefore the RCA's aren't getting a signal. Or, there could be a LOC - line out converter - somewhere in the jeep pulling the signals off the front or rear speaker leads and converting it to RCA's. I'd check behind the radio and see if the RCA's are loose back there. If not, I'd follow the leads from the amp and see where they go.
When my time comes, mix my ashes with gunpowder encased in brass, point me towards murderer's and pedophile's and let me fly.
(: ° ɹǝʌo ǝɯ 11oɹ ...sıɥʇ pɐǝɹ uɐɔ noʎ ɟı