I need to add an OBD-II based accessory to a OBD-port-less and ECU-less car

Question

My guess is the accessory would work fine if only provided power (no need for it to receive diagnostics info, just to turn on to perform its function).

Would it be possible to connect pins 16 and 4 to battery and ground, respectively, to have the accessory turn on?

Thanks for your help.