Can't get fuel guage or fuel pump to work. no bus code and code 920,921,&999 als

What is your question?

We changed ignition switch that fixd blowe and radio. truck would start n run then just shut off randomly or not start back after shutting off. we changed asd arelay but can't locate fuel pump relay. almost acts like relay or something gets hot n shuts down or a short. i also went thru unplugging cam n crankshaft and other sensors to narrow down what is causing bus code. thanks for any help