climate control module just buzzes
 

89 560SL 5 button control unit. I had the intermittent blowers problem that I traced (thanks to posts by other listers) to the solder joints in the climate control module. I found that the joints on the left side circuit board were weak. I removed the unit and could get the fans to start by flexing tthe circuit board on that side. I resoldered everything, tested it and it worked perfectly. So I put it all back together and reinstalled it; ready for some nice cool air here in AZ. And then when I started it up all it does is buzz. Inspection finds that the relay second from the left (when viewing from the pushbutton side of the unit) is not latching, but rather operating like a buzzer. If I manually close the relay on the right side of the board it stops buzzing, but the fans never start. So in effect the a/c is dead. How in the world could it go from working perfectly to this situation simply from reassembly? I have no idea. I see no bad soldering on the circuit boards. I see no places where solder may have run together causing a short. Could something "up stream" have been damaged? Does anyone have a pin layout for the two multiconductor connection cables so I could test to see if they have the proper voltage/ground etc.? Would this situation arise if one of the relays burned out/failed? P.S. the diodes seem to be OK testing with a volt meter. (conducts one way and not the other) Any help with trouble shooting this mess is greatly appreciated.

Solved
 

I had the multi-conductor cables reversed. Does not seem to have caused any damage. I thought the were keyed and could not be reversed. Wrong! Swapped them and it all came back on working fine. No more cutting out at random. So if you tackle this on your car, be careful.