85 Chevy c-10 305, Ignition module keeps burning out. WTF?

I just recently gave my truck a tune-up. Plugs, wires cap, the whole bit. The same day when I took it for a test run the ignition module burned out. Sine then I have replaced it three times after 2 burned out. The two I replaced lasted for three or four days and about 80 miles combined. Now I know that the module that the books call for my truck is either 5 pin or seven pin. Mine is neither of them. It only has four pins. The harness only has four tab connection for the module. I'm outta ideas. What is causing the module to keep frying?