Broke down

Left out and 1 mile away Truck shut off . Turned key on no dash lights or buzzer all other headlights 4 ways etc still working. Checked ecu fuse ok left key in on position wiggled wires to ecm nothing . Went to check fuse panel and suddenly buzzer came on. Started went back to T/S Any ideas ? I don’t know where to start. Worried ecm is on way out. Could it be symptom? Everything working good now no new active codes trying to change bulb to get stored codes now Thanks any ideas at all

 

I just realized Sorry was in a panic 2000 Freightliner Classic 12.7 DDEC lV. Acts like ignition switch unplugged all lights working except dash. Only active code is 46 low ecm battery voltage has been there for years. Also trying to change dash bulb can’t get front cover off. Strange thing is abs light came on right before problem occurred and has done it again just now as Truck is running . Abs light flashed once only. Just replaced front abs harness and other sensors and wires. Have 1 possible bad wire on Power distribution module inside fuse box, don’t know what people is for honestly. Could bad ground on frame near starter/ spring hanger be for ecm only? And starter lights all still work but ignition and dash lights ( ecm ) not work? Thanks to all

 

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Everything key on quit I’m not sure about blower motor. Truck is running this morning A/C won’t engage unrelated I’m guessing. Grounds look good wondering about 1 small ground being for ignition/ ecm it’s not loose I’m trying to wiggle ecm and battery wires to replicate