The GPS interface can be fed in 2 ways: with a stabilized 5V supply or with a 10 to 25V unregulated DC supply. In both cases the power is fed into the RJ45 connector on point 8. Pin 7 is DC ground. The power supply current is first secured with a slow 315mA fuse (in socket). Then there is a Transzorb device to ground. This device is a short-circuit for reverse polarity voltages and for voltages above 27V. It causes the fuse to blow and in doing so, protecting the other electronics and GPS module.