I've tried a lot of research but I can't find specifically what I'm looking for no one has actually mentioned this and I've looked at various wiring diagrams which still don't prove how this is possible:

I understand that the alternator supplies electrical current for the vehicle electronics when the engine is running as well as charging the battery.

However, when the battery is removed, the electronics still operate for a while (although this is dangerous I know) as the alternator is powering the electronics.

My question is how is the alternator directly powering the electronics without the battery??

All the wiring diagrams I've looked at show that the alternator is powering the electronics through the battery but if this is removed shouldn't the electronics shut off as the computers etc have no battery voltage?

Is there some sort of direct connection between the alternator and vehicle electronics?

  • 1
    I'm thinking that the alternator is charging the battery through the direct positive wire which is connected at the terminal, the power from the battery is then flowing through the other end of the terminal and when the battery is disconnected the power from the alternator then skips the battery and effectively becomes the battery positive.
    – TMax
    Apr 6, 2020 at 11:02

1 Answer 1


When you follow the wiring diagrams, the alternator is directly connected to the battery (if that connection fails the the alternator can be damaged) and the battery is connected to the vehicle electrical system.

The common point is usually the battery positive terminal or the other end of the battery positive cable.

Removing the battery still leaves the vehicle electrical system connected to the alternator. It can work fine, it can damage the alternator - I strongly advise not disconnecting the battery while the engine is running: I have replaced too many alternators for customers in the past who have made that error.

  • 1
    Just to add here, the alternator and battery are wired in parallel meaning that the power doesn't have to go through the battery to reach the rest of the vehicle.
    – Techlord
    Apr 7, 2020 at 2:14

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