PLEASE HELP! Electronic problem V3500

[sand_in_my_ears]

PLEASE HELP! I have a 89 GMC V3500 4x4 TBI 454 TH400 Crew Cab Dually 150k miles. It has duel tanks but only the left (original) tank is cleaned with a new pump and sending unit.
PLEASE read before commenting.
I'm having FUEL PUMP and overall starting problems. I was driving steadily at about 70mph and the truck instantly lost power (engine shut off). I was able to get to a stop and off the freeway. I tried to restart my truck a couple times and then I went completely dead (no power), the lead negative ground cable end melted at the battery. It got towed home. I replaced the negative cable. I jumped straight to the fuel pump and it worked fine but still wouldn't start. I was able to run the engine great using a can of brake cleaner. THIS IS WHEN THE FUN STARTS! I replaced the fuel pump relay, no change. I tested all the fuses and found a blown "ECMB" fuse and replaced it. I then jumped the pump power wire at the relay, no change. I checked continuity on the on this output wire and got a seemingly dead short, I question this result. I checked the 12v relay power wires and got a full 12v. STRANGLY, I only got 0.6v coming in to the relay on the ECM pump signal wire, it is supposed to be full 12v. I checked the ECM output fuel pump wire (the one going to the pump relay) and got a continuous 01.9v for 20 seconds. So the voltage coming out of the ECM might be a very weak, it dropped more then a volt while going to the relay. I also replaced the tank toggle switch on the dash, it just needed it. I have a new fuel tank selector valve (the one at the fuel tank) but haven't installed it.
SO IN CONCLUSION
1. Engine quit
2. Negative cable melted
3. ECMB fuse blown, replaced
4. Fuel pump runs, but doesn't make the engine run
5. Engine runs great on brake clean
6. ECM pump signal wire very low voltage
7. Replaced the pump relay
I am going to be back on here at around 1 or 2 pm pacific time (Las Vegas). Thank you for your help.

 

[sand_in_my_ears]

Things that I need to check. ECM power, possibly shorted, but the engine runs. Oil pressure switch wires shorted. I need to figure out where the fuel pump wire goes to from the relay, so I can run a wire to bypass it. I'm not good with electronic stuff. I'm a tool and die maker. Give me a chunk of steel and a mill anyday over electric anything!

 

[Camar068]

I'd start with checking all your grounds. After that, I'd look at the 12v signal your expecting from the ECM (don't know if thats correct or not....just helping troubleshooting electronics in general).

just in case, in issues like this put the negative lead direct to the battery negative...if needed extend that negative meter lead with known good wire so you can get where you need with the meter.