Truck Repair: Fuse blowing, oil pressure switch, fuel pump relay

Question
-------------------------Hi Van its a full size blazer and its the ecmb fuse like you said since its a full size truck with a 350 will it make a differences.  thanks again
Followup To
Question -
Hi Van I have a Chevy 1989 V10 Blazer 4x4.  My problem is this for some reason it wants to blow the fuse thats marked ECM2 and when it does it wont start or if its running it will turn off.  It doesnt do it all the time, like yesterday I drove for a couple of hours then it happened so I had to have it towed home.  I put a new fuse in and watched while I started it, it will blow as soon as the engine starts.  Any ideas where to look?
Answer -
Hello Tony,
I assume you mean "S"10?
Engine size makes a little difference, but lets say a 2.8 L V6...the fuse marked ECM B supplies power to the ECM obviously, but also to the fuel pump circuit, including the fuel pump relay, and the oil pressure switch which also runs the fuel pump, and all the wires and connections associated with getting power to the fuel pump.
Check that fuse with the ignition off, since it shows to be hot at all times.
If you want to isolate the fuel circuits from the ECM circuit, find the fuel pump relay, and the oil pressure switch. Disconnect the orange wire form each, actually from both, and then create a fused jumper to connect battery voltage to the relay, or later to the oil pressure switch, but just to see which fuse blows.
A short in the fuel pump or pump control wires will blow the temporary fuse.
If the ECM B fuse still blows, some deeper tests will be needed...maybe just wires to the ECM, but lets hope for the fuel pump...maybe just that oil pressure switch.
Van

Answer
Hi Tony,
It's the "V" that is throwing me...usually the full grown ones are "K"...do you happen to have a V10 engine???New one for me if so.

But, at any rate, if it is like a pickup, that fuse and wiring are about the same as far as oil pressure switch and pump relay, except for two differences that I know of.
Some applications actually have a second fuel pump relay, called a redundant relay...in addition to the oil pressure switch, which is a redundant pump power system for almost all GM vehicles with injection.
The other difference is on the full size pickup, the fuel pump fuse is in a holder under the hood, on the firewall, passengers side, near the fuel pump relay.
Ouch! that didn't help you any there.
I don't have that manual here, but I believe that fuse is on the PUMP side of the relay and oil switch, and I don't know if the orange wire to that relay is from the ECM fuse, or straight from the battery someplace else.
A test light, and pull your blowing fuse would tell pretty quickly.
Van