Van just stops running with intermittent spark

I have a 1993 Chevy Astro Van 4.3L CMFI. Put new fuel injectors in and van was running good. Then while driving van would stop running. Wouldn't start. Erratic spark. Replaced coil, spark plugs, distributor cap and rotor. Also replaced Battery as it was the wrong size. Van then ran but began not starting even with spark. Put in new fuel pump, filter and relay. Ran great but later began the same problems. Would just die while driving. Check engine light came on and I was able to retrieve the following trouble codes. 43 Electronic spark control unit. 54 Low fuel pump voltage. (What exactly is that and what does it mean and how do I fix it?). Intermittent problem for awhile but when running ran great. Here is what is my current problem, while backing down my driveway Van just stopped running. Decided to try starting it one day and it started like nothing had happen. Drove it half a block and it died. Won’t start. It turns over but nothing. No lights, no horn, no radio, no interior lights and I do not hear the fuel pump kick on. Replaced fuel relay again but still nothing. I get spark but no fuel. It appears their is not voltage to the fuel pump. I have attempted to try and locate a short but am having difficulty. Can you give me some advice in detail how to systematically trouble shoot this problem in layman's terms. Electrical problems are not my strong point. Please help me before I loose my mind. Thank you.