Where do you connect the B+ wire, and what color is B+?
B+ (well done)
B+ is not a grade but an identification of the use of a connecting wire on an Android headunit install. B+ is short for Battery + or Battery Positive.
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: to supply a permanent 12v live feed to a device in the car. The B+ should continue to live even if the key is removed from the ignition, the car is locked, and the alarm is set.
Very often, a YELLOW cable is used to identify the BATT+ wire on an ISO lead. Not all vehicle manufacturers use the ISP colors. But the patch leads, CONNECTS2, and universal fit Android headunit leads should be YELLOW for B+.
A permanent live (B+) is used to power the alarm system or keep the remote central locking ready to listen for its plip. The use of an android headunit is to keep memory refreshed and is 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 is colored Yellow. You can identify the B+ wire or an alternative candidate to use as a B+ wire by finding a live circuit 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 common if you need to draw much more power than the original factory radio. Usually, an amplifier would have a heavy gauge custom fused feed to the battery terminal to give the B+ wire needed.
B+ is also called Battery Live, Battery Positive, Yellow Wire, BATT, BATT-12V, or anything that indicates it is directly connected to the car battery.
Some vehicle manufacturers use plugs and sockets that look like ISO standards and 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 can modify this out-of-band behavior for B+ in these situations (a yellow flying lead is often used).