BATT+ wire on the android headunit

Where do you connect the B+ wire and what colour is B+?

B+ (well done)

B+ is not a grade but an identification to the use of a connecting wire on an android headunit install. B+ is short for Battery + or Battery Positive.

Battery +

B+ or Battery +, BATT12V, BATT-12V, LIVE, also known as permanent live, battery backup or memory live. These wires are all there to achieve one thing. That is to supply a permanent 12v live feed to a device in the car. The B+ should continue to be live even if the key is removed from the ignition and the car locked and alarm set.

Yellow wire

To identify the BATT+ wire on an ISO lead, very often a YELLOW cable is used. Not all vehicle manufacturers use the ISP colours. But the patch leads, CONNECTS2, leads and universal fit android headunit leads should be YELLOW for B+.

Permanent live

A permanent live (B+) is used for things like powering the alarm system or keeping the remote central locking ready to listen for its plip. The use in an android headunit is to keep memory refreshed. Particularly useful for the fast boot models. Without a permanent live (memory live or battery backup) they would have to start cold each time and miss the fast boot. A permanent live (B+) connection makes the power available to your android headunit before the key is turned in the ignition. See our ACC wire post to complete the ISO power pair.

Where is the B+ wire?

The B+ wire is often found on the ISO power plug in position A4 and coloured Yellow. You can identify the B+ wire or even a alternative candidate to use as a B+ wire by finding a circuit that is live even with the key removed from the ignition. If you need to install a new B+ because your car doesn’t have one suitable, then picking up a feed from the vehicle battery + terminal is the place to go.

Custom B+ installation is quite common if you need to draw much more power than the original factory radio did. Usually an amplifier would have a heavy gauge custom fused feed to the battery terminal to give the B+ wire needed.

Other Names

B+ is also called Battery Live, Battery Positive, Yellow Wire, BATT, BATT-12V or anything that would indicate it is connected to the car battery directly.


Some vehicle manufacturers use plugs and sockets that look like ISO standard and they fit standard ISO plugs. But the wiring for ACC and B+ may not follow the standard ‘key in the ignition’ and direct battery routine. This is due to computer control of the power in the car and B+ wire may not behave the way you expect it for some models such as later Volkswagen Group cars, Peugeot 106, Vauxhall Astra, Citroën C3 and some JCB tractors. Adaptors are available to modify this out of band behaviour for B+ in these situations (a yellow flying lead is often used).

BATT + wire on android headuit
It is important to get the yellow battery+ wire connected correctly for your android headunit to function.

Other wires in this series

Wires in the speaker connections series

An staff blogger. I am a multi-skilled dogs-body and I also make the coffee ☕

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