No Check Engine light when I turn the key to the on position

My vehicle is a 1991 Isuzu 3.1L V6 4x4. While driving down the road one day, the vehicle just quit running. Checked all fuses / relays, all checked out. Not getting fuel, so I assumed the fuel pump was out. I pulled the tank, then the pump and tested it and it pumped gas. After installing the tank and pump, I noticed the check engine light was not coming on when I turned the key to the on position. That is where I stand. For the previous month, I noticed the oil light coming on at low idle, and off at high idle / driving. Not sure if there is a connection, but maybe. First thing I did was replace the ECM with a used one from a salvage yard. Still no check engine light. The truck starts off of starter fluid. Still no gas. I also replaced the oil pressure switch and ECM relay. Both fuel pump relay's close properly when voltage is applied across the inductor side. I check the check engine light led in the instrument panel an it is good. I ohm'ed out a few of the main power lines going to the fuel pump and ecm, all checked ok. Is there another switch or relay that could possibly be disfunctional causing the system not to provide the correct signal for the ECM? It could be possible that this ECM is defective as well. Or both could be good and my problem is somewhere else. I don't want to take it to a mechanic because I am my own mechanic, but this one has me stumped. Any help is appreciated.