1993 Chevy Hd Heater Control Module.

The heater control module didn't have a LED display so I checked the fuse and it wasn't blown. So i checked to see if it had power to the module and it did. When I touched the DC test light to it the light it lit up bright and I also put a meter on it and it had 12 volts. I tested another part of the plug and the blower motor came on. So I took the module and cleaned up the end where the plug goes on, plugged it back in and it came on. then I went through the blower motor speeds, low medium and high and it went off. so I figured the module wasn't any good and I went to the salvage yard and got one out of a 94 truck. It didn't work so I just thought it was the module from sitting around in the weather. I went to another place and picked up one but it doesn't work either. Could the problem be in a relay or anywhere else?