Hello i just bought a used 2005 dodge ram with an Rb4 radio, at first the battery was dead so i bought one new when i connected the battery i went inside the cabine and turned on the radio and it did fine, when i took the key of the ignition for about 10 seconds, then i placed them again in on and tried the radio and it did not turn on like the first time, then i went to the hood and removed the negative battery cable and connected it back right away and went to the radio and this time it did start on, to make the story short when i disconnect the battery and connected it again the radio turns on but when i remove the key from ignition for 10 seconds and then plaxce it back again to start position the radio does not turn on what could be the problem help me please

Car Audio & Video - Dakota - Dodge RB4 Navigation, CD, AM/FM, with CD Changer Controls