Nothing ruins a good cruise like a ride home on a flatbed. That’s the situation Mike Montanari from Fast Monty’s Garage found himself in after his car died, forcing him to track down what he believed was a bad One-Wire alternator. He filmed the whole diagnostic process, sharing some old-school wisdom and a few warnings for anyone working on a modern charging system.

The Right Way to Diagnose a Charging Problem

The first thing Mike did was warn everyone against the old-school trick of pulling the battery cable off a running engine. “Don’t do that anymore, guys,” he stressed, explaining it can fry modern electronics. Instead, he showed the right way: check the battery voltage with the car off (his was 12.5V), then start it and check again. The voltage is supposed to jump to 14V, but it dropped to 11V—a dead giveaway that the alternator was shot.

A Hot Clue and Installing a New One-Wire Alternator

While testing, Mike found another clue: the old alternator was getting screaming hot, which he learned could be a sign of a bad ground. “Turns out that if your alternator is hot like that, it might not be grounded properly,” he said. He tried adding a dedicated ground wire to the old unit, but it was still dead. That led him to install a new 160-amp Tuff Stuff One-Wire alternator, which immediately solved the charging problem and started putting out a healthy 14 volts.

The Most Overlooked Step in an Alternator Upgrade

But the job wasn’t done yet. Mike pointed out a huge safety issue that most people forget when upgrading to a bigger alternator. “When you upgrade your alternator to a higher amperage, you also need to pay attention to your charge wire size, and mine’s not big enough,” he explained. To safely handle the extra juice from the new 160-amp unit, he swapped out his undersized 8-gauge charge wire for a heavy-duty 6-gauge wire and a bigger 200-amp fuse using a Painless Performance kit.

More Than Just a Simple Swap

The whole process showed that a simple alternator swap can be more complicated than it looks. A proper One-Wire alternator setup needs a good ground and a charge wire that’s big enough to be safe. It’s a complete electrical upgrade, and Mike’s experience is a great lesson for anyone tackling the job.