I just recently replaced the transmission in my 1996 S10 4.3 liter blazer and was able to drive it around a bit before I started debugging an electrical system problem. I had a constant 4 amp draw and before I discovered what caused the drain, I would disconnect the battery at night so I could start the engine in the morning.

I pulled all of the fuses from the fuse box and put an ammeter inline on the positive side of the battery; then I put each fuse back in one at a time and checked the current drain. Turned out to be the courtesy light circuit that was causing the drain, (the tailgate light wouldn't turn out). I replaced the switch and everything appeared to work correctly.

However, when I tried to start the engine, the ignition fuse (#5) pops immediately after the ignition switch is turned on.

According to a local mechanic, by disconnecting and reconnecting the negative post on the battery I may have blown the computer.

Before I spend the money on a replacement computer, does anyone have any suggestions?

 

I browsed the forum and found some awesome helpful hints by swartlkk. I removed all components in the fuse 5 circuit and was able to determine that the O2 sensor in front of the catalytic computer had shorted out (probably the heater element) and this caused the fuse to pop.

I've since put in a new O2 sensor, MAF sensor and cam position sensor and successfully passed emissions testing. So once again, my Blazer is running well and hoping to get 350K plus out of her before the next major work. It's currently at 272K and so far I've put a new engine and transmission in it. It's a lot of work but still cheaper than a car note.