hey guys, i just installed a head unit into a truck i just acquired, and now it is not producing any audio. the truck only has two speakers, is there any chance that the HU needs a full load of speakers for it to operate? it is powering up, reading cds, the audio out bar graphs are moving, but the speakers aren't working. i've rechecked the connections several times, perhaps i need a dummy load for the rear speaker outs? any ideas? thanks guys.