I'm having an issue starting my 88 lxi. I replaced the engine with one I rebuilt and have not been able to get it to start since. It cranks and has spark, but no fuel. The fuel pump does not come on unless 12 V manually applied to it. I also verified that the main relay works correctly when voltage is manually applied to the appropriate pins on it.
I narrowed it down to the main relay harness connector. The IGN SW pin is not getting properly energized to start the fuel pump. I verified that the actual ignition switch is working correctly in each key position.
IGN SW relative to the GND pin on the harness reads -0.5 V with key off and 0.6 V with key on
IGN SW relative to the battery negative post reads the correct 0 V with key off and 12 V with key on
GND harness wire reads 0.5 V relative to the battery negative terminal with key off
I'm having trouble tracing the harness through the firewall into the engine bay. Is anyone familiar with where this wire would ground to in the engine bay. And what would cause the GND wire to have a voltage offset like this? I would think that if it was shorted it would just be 12 V. Any help is appreciated.
Summary: GND wire in main relay harness has 0.5 V with key off and 11.5 V with key on. This is preventing the IGN SW from generating sufficient voltage to activate the fuel pump relay. Not sure what would cause this on the GND wire