From http://www.garmin.com/products/gps35/

GPS35-LVS Attached 10 foot power/data cable with bare wire ends. Accepts power from
unregulated low voltage power supplies between 3.6 and 6 VDC. Asynchronous serial data interfaces
via 2 serial ports with true RS-232 voltage level outputs.*

GPS35-HVS Attached 5 meter power/data cable with bare wire ends. Accepts power from
unregulated high voltage power supplies between 6 and 40 VDC. Asynchronous serial data interfaces
via 2 serial ports with true RS-232 voltage level outputs.*

GPS35PC Attached 10 foot power/data cable with female DB-9 serial connection, ready to attach to
your PC. Additional 8 foot power cable extension from the DB-9 connector terminates in a cigarette
lighter plug for easy application of power supply voltage between 6 and 40 VDC. Asynchronous serial
data interface via a single serial port with true RS-232 voltage level output.* **

*All serial inputs on all versions are compatible with either true RS-232 or TTL/CMOS voltage levels.
Port 1 uses NMEA 0183 data format. Port 2 transmits binary position and raw measurement data and
receives RTCM SC-104 differential corrections data, message types 1, 2, 3, and 9.



So the "low voltage" and "high voltage" numbers are clarified there, and the 35PC version just has the car adaptor plug instead of an unterminated wire. And just one serial port outputting NMEA, instead of one with NMEA and a 2nd one outputting binary data. Who cares?!?

So I guess the one I want is the high voltage one without the car adaptor. Since the 12V coming from the Empeg is within the 6V-40V range, it sounds like it's a no brainer.