Intermittant "no spark"

[HelixHockey]

My daughter has a 91 Explorer with a V6. The problem started with a dead battery one day. I thought the fuel pump went bad and drained the battery. Turns out it froze. Even with a charger/booster hooked up the car wouldn't start. Replaced the battery and it started. Then the battery went dead again after the car sat a day without use. Sears tested the battery as "bad" and warrantied it. The car started and ran fine for a bit. The battery drained again. Then would not start even with a charged battery. I have an inline spark detecting light and the explorer showed no spark. I hooked the light up to another car to check it and it works. Hooked it back up to the explorer and it started, the light flashing to show the spark. Scared the hell out of me. When putting a test light between the negative cable and negative terminal, some times it shows a draw when the key is not on. I went through fuses to see what circuit the draw was on and it showed it was the ECC relay fuse under the hood. Now I keep the battery charged and sometimes the car starts and other times not. It seems it may be temperature related as it has been fluctuating between single digits and the 30's since December. I think the times it wouldn't start, it was colder out. I tried to think of every detail, hope someone can help.

 

[MrShorty]

The EEC fuse protects quite a bit, including the main computer, ignition control module (which controls spark), fuel pump in part, and so on.

The first thing I might do in this situation would be to pull codes from the computer and see if there are any clues there. You might also start unplugging segments of the engine management system (get a wiring diagram) to see if you can isolate the draw to a specific component.