Which Cummins do you have?

The 5.9L ran from 1989 to 2007 in two very different forms — the mechanical 12-valve 6BT through 1998, then the electronically managed 24-valve ISB from 1998.5. The common rail arrived in 2003. The 6.7L replaced it from 2007.5.

The 1998 model year split mid-production, and 2007 had both the 5.9L and 6.7L available. Confirm your engine rather than ordering by year alone.

Why Cummins owners upgrade

The grid heater on these trucks pulls hundreds of amps on a cold start, which is why dual batteries have been standard throughout. The factory alternator is sized for that and little else.

Add a plow, an inverter, a winch, auxiliary lighting or an audio system and the shortfall shows immediately. Older trucks compound it — a thirty-year-old alternator is unlikely to be meeting its original rating.

Single wire turn on

Older Cummins trucks are often rewired, swapped or running a modified harness. Single-wire turn-on alternators self-excite and need only an output connection, which removes the factory excite circuit from the equation.

Dual batteries

Replace both at once and match them. AGM copes with diesel vibration far better than flooded lead acid, which matters on a truck that has been working for decades.

Don't skip the wiring

See our Big 3 wiring upgrade guide and Big 3 kits.

Browse all Mechman high output alternators or shop by vehicle.