OBD‐II plug guide - fochica/fochica-wiki GitHub Wiki

An OBD-II socket is a standard 16 pin socket that is common in new cars. It is located near the steering wheel and has a pin for 12V constant power line. On one hand it is a source of constant 12V that doesn't require modifications. On the other hand it is far from where the child seats are.

What you should have in your car is a female socket, which has a horizontal groove and female pins:

What you need is an OBD-II plug, which has a horizontal groove and 16 male metal pins:

Pin 16 is 12V
Pin 4 is chassis ground (preferred ground)
Pin 5 is signal ground

The other pins are used for car's computers and communication protocols, such as CAN. Do not mess with those connections unless you know what you are doing. See Wikipedia for more information.

Note that you may need to rotate or flip the diagram depending on whether you are looking at the plug, the socket or depending on the orientation of the part. Always verify that you have the right pins with a multi meter.

Based on the specification, the 12V pin can provide up to 4A of current, which is more than enough for the default Fochica builds. If you have made alterations, please verify your current requirements.

Verify with a digital multi meter that 12V is available on pins 16 and 4 and that power is supplied even if the key is not in ignition.

See how much physical space you have for the plug so not to create a physically uncomfortable situation for the driver once installed.

Search for "OBD male plug". Look for plugs that fit your physical space. You may end up cutting the box or using the PCB part without the box due to space constraint.

If you want a plug that comes with pre-attached wires, search for "OBD male plug pigtail".

The two photos below are of the most popular plug type. This is a good quality plug, with places to solder the wires and strain relief for the cable. Unfortunately it is quite long at 12 cm and will most likely be protruding in an uncomfortable way. You may want to use the connector and PCB parts by themselves and build some alternative protective housing for the cable.

The next two photos are of another plug form factor that is more compact and has the wires exiting at an 90 degree angle. Note that the pins are less comfortable to solder to and that there is no strain relief for the cable.

Here is a typical OBD-II device that is an ELM327 clone. If you have one lying around without use, you can just open/break it and use the housing and connector as the power plug.