Going nuts with my '94 E420

Trying to fix the antenna this morning (no luck) and I notice something odd. First, the radio comes on, but nothing out the speakers and then I notice that the courtesy light won't go out. I fiddle around, start the car and note that the battery is a bit weak, start again, slow cranking, start again, just a click.

OK, charge the battery, still just a click. Found a bad fuse, replaced it. Swapped batteries with a known good one (from my other running Mercedes, same battery type). Still just a click. Then nothing, no click. The rest of the car's electric are working, lights, radio is now fine, (and even the damn antenna now). All the dash lights working, car ran fine yesterday. The bettery works fine in the other Mercedes. Checked all the fuses, even the ones in the base module. Disconnected and reconnected the battery, still won't turn over.

I'm going nuts, any suggestions? (PS I replaced the wiring harness about a year ago, so I don't think that's the problem).

Oh yeah: with the ignition on, air recirc is blinking. Is it supposed to do that?