[Art]

Need help, 2006 Ford Focus ZXW, When I unplug battery, car keeps running but lights flicker. Replaced alternator and installed new battery, but lights still flicker. What could it be?

[John]

Unhooking the battery whilst the engine is running may have been a great test back in the 1970s when there were points ignitions and carburetors, but ecu’s, PCM’s, TCM’s and all sorts of other very small circuit-boarded pieces don’t necessarily like to see big electrical spikes.

Don’t do this.

[Christopher]

Stop doing that!

[Steve]

Never unhook the battery with engine running.
What lights flicker?

[James]

Why would you unplug the battery with the vehicle running? This isn’t a vehicle from the 1970s that doesn’t have modules.

After you most likely destroyed the Power train control module, you will then find the alternator is controlled by that same module.

Not having a clue what you are doing makes it even worse.

I could explain what to do, but you wouldn’t comprehend.

Tow it to a shop that knows what they are doing before you do anymore damage.

[Derrick]

So instead of cooking every module in your car, how about we head to the store and buy a good multimeter, making sure to buy a model capable of reading amps DC with what looks like a clamp on the end of it.

After you spend that $200-300, come back, and we’ll teach you what to do with it.

[James]

The harness to the voltage regulator is probably broken 3″ back from the connector. After confirming that, the connector pigtail needs to be replaced, but please by all means, keep wasting money, because “I can’t afford a Mechanics”.

[Alec]

You should absolutely never disconnect the battery while the engine is running on any modern, computer-controlled vehicle.

[Nick]

Disconnecting the battery while the engine is running is a good way to mess up the cars’ electronics. Nice upsell!

[Author]

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