Power + charging
Battery → starter (cranks engine) → alternator (recharges + powers system, 13.8–14.5V at idle). Load-test battery; output-test alternator under load.
Modern vehicle electrical isn't '12V plus accessories' — it's a network. Knowing the network beats guessing every time.
Most electrical chases are ground problems. Check grounds first, modules last.
Battery → starter (cranks engine) → alternator (recharges + powers system, 13.8–14.5V at idle). Load-test battery; output-test alternator under load.
Modern vehicles run 30–80+ modules on CAN buses. A scan tool that talks to all modules is non-negotiable. Module no-comms usually = power/ground at the module, not the module itself.
Acceptable draw: <50 mA after modules sleep (10–30 min). Pull fuses one at a time with an ammeter to isolate.
Three suspects: failing battery, alternator not charging, parasitic draw. Test in that order with a multimeter or smart charger.