Chevrolet Repair: silverado heater control module, negative cable, ground cable

Question
I have been having problems with two issues on my 91 Silverado.  The first problem was the battery would discharge after setting for a couple of days.  The truck could be jumped off or the battery charged and it would start and be fine if driven daily.  I checked the alternator (tested good both on and off the truck) and changed the battery.  
I began to disconnect the ground cable as part of a troubleshooting regime to determine if the battery I had purchased was the culprit.  I hooked the negative cable up and the truck started fine.  The next morning it wouldn't crank.  I found the battery cable loose and tightened it up and discovered the heater control module was not lit up and did not function although the truck had started.  I replaced the module with a used one and all seemed well for several days of operation. I put the truck up for a few days due to scheduling with the negative cable unhooked to prevent the battery discharging.  When I hooked it back up the truck started but the replacement heater control module failed again.  
I resolved the discharging problem (glove box light staying on) this weekend.  The system went from .25 amp draw to 0 and after setting hooked up for a couple of days the truck started right up.
Now I am afraid to install yet another heater control module without some certainty that I am not doing anything to cause it to fail or that I need to check anything else out.  I cannot find a wiring diagram for the module.  Everything worked as it should with the last module.  What checks do I need to make to certify that I will not use up another module?  This doesn’t seem to be a common problem but it is happening too often for me.  Thanks a lot for your help!  

Answer
Hi Clark, Good find on the glove box lamp. I wouldn't worry about the heater control head again, just replace it. The sun and moon must have been line up with mars and this caused the problem. Really, I see nothing that could have caused this to happen.

Have a Great Day          Mark