kenny's are known for being very sensitive with their protection circuit...
sometimes its pretty easy to find the bad speaker, sometimes its a pain in the ass.
does it do it right away or fairly consistently? or does it only do it every once in a while?
if its the former, then it should be pretty quick to track down. most of the time, the instant there is a problem and it shuts off, one of the speakers will usually make a "pop" noise, or when you reset it and it turns back on and instantly goes into protect. if its only one speaker making the pop, that is usually your bad speaker (or channel with bad wiring) remove the speaker for a while and see if the problem goes away (or just disconnect both the positive and negative wires from the radio).
if the problem is with the cars wiring somewhere, you can also use a meter to check for continuity to ground down each speaker wire at the radio harness, if a short to ground is the problem, you will see it here, the wire with the extremely low resistance to ground will be the one shorting out, also both wires for that speaker should read continuity to ground of that is the case, but one of them should read about 4 ohms higher than the other, the lower number is the bad wire, the higher number is the other wire being grounded and then traveling through the voice coil and back down the other wire. that is why there is about 4 ohms more resistance.
but if the speaker is blown or damaged from water getting into the door and soaking the speaker (seems to be more of a ford and Chevy problem than most cars) you can check the resistance between the positive and negative wires for each speaker, you should see a number very close to 4 ohms but usually in the high 3's, if you see a speaker that is very low, usually below 1 ohm (but may be anywhere below 2 ohms) then that speaker is bad and needs to be replaced
now if the problem is the latter and only happens every once in a while like you may be able to listen for an hour or two with out a problem and then it shuts off, its probably going to be a lot harder to find as the meter test probably wont show anything 95% of the time. the first thing I would do would be to turn the volume up only 20%-25% of the way and play some good clear music, preferably something with made with only real instruments and nothing with any kind of digital noise or sound effects added, then one by one put your head close to each speaker and listen for one to have a slight amount of distortion, if they all sound great, try again this time with the volume only at about 10%... when a speaker is going bad, a lot of the time it may be easier to notice at much lower volumes. if it is a wiring problem, then that wont work, the easiest way would be to disconnect one speaker at a time and drive around listening to it until you disconnect the one speaker and the radio plays fine with out shutting off.