Electrical
No crank, dead batteries and charging problems
Most 'bad starter' calls are a voltage drop through a cable or ground. Ten minutes with a meter tells you which side the problem is on.
The answer
Test sequence
- Measure resting voltage at the batteries. Roughly 12.6 volts is charged; below 12.4 is discharged, not dead.
- Load test each battery individually. One shorted cell drags the whole bank down.
- Voltage-drop test the positive cable while cranking — more than about half a volt is a bad cable or connection.
- Voltage-drop test the ground path from battery negative to starter housing. Same limit.
- Charging output at 1,200 to 1,500 rpm should be roughly 13.8 to 14.4 volts. Low output with clean cables means alternator or regulator.
Parasitic draw
If it dies overnight, measure current draw with everything off after the modules go to sleep. Pull fuses one at a time to find the circuit. Aftermarket inverters, radios and APU wiring are the usual culprits.