So I was tracking a large draw in my 89 blazer that was causing some fireworks and not allowing me to start it. After having narrowed down a few obvious problems I was still getting an 8.1-8.15 volt draw with everything off. I managed to eliminate this, or at least drop it down to 1 and some change by pulling the ECM B fuse. Cool, but the trouble is I have no idea what is in this circuit, where to follow looking for shorts, what I should fix, etc etc, and I can't find a decent enough wiring schematic to help. All the homemade and chiltons/haynes diagrams are woefully inadequate and the factory ones are prohibitively expensive. As I have very little experience working with ECMs, particularly of this vintage, I really don't know where to go. Any help from the resident electrical gurus/early GM engine computer experts would be fantastic. I am working on a budget, so I don't want to go ***** nilly buying stuff and hoping I fix it if there is an easier solution.

 

It's an orange wire that splits off into 5 different orange wires, 2 go to the ECM, 1 to the oil pressure switch/sender, 1 to the fuel pump relay and 1 to the redundant fuel pump relay.

 

Awesome! Thanks. I was trying to chase it myself but it got real confusing in that rats nest of wires that used to be a factory wiring harness. One further question though: am I safe in assuming the ECM itself is probably not causing the short if pulling the ECM 1 fuse didn't do anything? In other words, am I still probably looking at a wiring issue or at least a component somewhere in the ECM B circuit and not looking at replacing the ECM?

 

First, I'd check the relays since it won't start and you're getting a check engine light. Is the fuel pump coming on? It's possible a relay has shorted out causing the big draw.

I'd use a digital multimeter and check out each wire and make sure none are chafed and shorting out.

Since the oil pressure switch and relays have one orange wire each, those will be easy to trace. But the ECM has two orange wires coming from the same source. They are pins: C16 in the C1 connector and B1 in the C2 connector.

 

Thanks a truckload man, that really helps me narrow down what I feared would be endless wire chasing. My cheap little 25 buck craftsman multimeter is finally getting some use these days, though, so if anything at least I have an excuse to play with my toys.

I agree on the fuel relays first as well, since I haven't been hearing anything kicking on or clicking when the key is turned to start. Plus, if there were a break in a wire in that area it might explain how I was getting shocked when reaching into that region prior to everything going completely dead. Again, I really appreciate the help, you pretty much answered my question perfectly. With any luck I'll be getting her stuck in mudpits before the official start of summer!

 

You were getting shocked? There's a good hint.

Put each hand on a battery terminal.. feel anything? Probably not. Unless you're a very sensitive guy.

If you're getting shocked, it's from a relay or motor circuit while the relay or motor is being de-actuated. When you turn off a coil that had 12volts applied the magnetic field collapses and that generates a voltage in that coil. It's called 'back-emf'.
Rule of thumb is that a coil drawing 2 amps at twelve volts will provide 120 volts at .2 amps at the switch or end of circuit turned off. It's not really that much volt or current but gives you an idea.
So lets say you have a bad wire to your starter solenoid and you put your hand right on that bad spot or break while the key is turned to crank. When that wire spot opens up, you'll feel a pretty healthy jolt if your body is touching the car.

It wont kill ya.. but you can get some good bruising from the reflex jump-back.

 

petty, appreciate the technical info, electricity is not one of my strong suits, and I am always trying to learn. In mechanics or construction I have inevitably come to the point where my limited understanding of electrical has become a limiting factor on a given project.

I was getting a jolt while adjusting my distributor actually, but there is a massive bundle of wires and stuff in that general area, so who knows what I actually touched to get the shock. Part of my reluctance to learn about electricity, ironically enough, has been my profound distaste for being electrocuted, however my ignorance tends to cause that to happen fairly frequently in my travels and projects. Fortunately since I am relatively used to minor jolts, I didn't panic and fly off the truck onto my floor via the toolbox and a table covered in carburetors....the second time