Originally Posted by arctictraveller
Is it possible the unit is wired to the house batteries, which are dead. If the separator wasn't working, starting the engine wouldn't help. Just a guess.............
That's kinda what I was thinking. If I recall from when I wired my Kenwood (similar model), there is a wire that goes to an "always on" low-draw trickle source that keeps the memory in the unit alive and also lights up the small red "security" light. In my SMB I wired this to an unswitched, always-hot wire from the main van (i.e., wired to the van battery). The radio itself is wired in SMB's funky way through the switch in the back and gets its "main on" power through that. I assume yours is wired similarly. When the stereo is turned on, the "main on" power takes over from the always hot trickle source and the small red security light goes out.
So, first, do lights and whatnot that get their power from your house batteries work? If so, then your house batteries are likely OK and not the issue.
When you say you "turn the switch in the back on," have you tried it on the setting for both the house batteries and the main van battery? (It's a switch with an "off" setting in the middle, a position for the house batteries on one side, and a position for the van battery on the other.) If not, try it "rocked" to both sides to see if one works. The other possible culprit is that this switch is bad. The fact that you hear a click up front and the red light goes off makes me think that maybe some power is getting to the main unit, but not enough to actually power up the full display and operations (although I'm not sure what the culprit would be). Try pulling the rear switch out and checking all the connections for corrosion and tightness. There may also be a relay attached to that circuit; I honestly can't recall offhand. If so, that may have gone bad, too. It's easy to replace if so.