Electrical problems with 94 Chevy Astro

I have had my 1994 Chevy Astro van AWD (115,000 mi, V-6, vortec, 4.3L) for a little over a year now. For about the last 11 months, I have had an issue with the check engine light flashing on and off. Usually this happens when I turn the headlights on, but they do not necessarily have to be on for the problem to occur. When the check engine light flashes, the van will falter and try to shut off. Most times it redeems itself and stays running but there are times when it will just shut off. We have replaced the distributor cap and rotor, the battery cable, the alternator, and the fuel pump and filter. On occassion, it will just crank when you try to start it. We have isolated the problem to a junction box located on the firewall directly on the other side of my headlight switch. It contains several fuses and is connected to 3 or 4 red wires. These wires, when wiggled, will make the van perform the symptoms mentioned above. The bottom left wire also gets so hot you can't touch it. I am now melting fuses and experiencing these problems more frequently. We are clueless. Help!