Hi: I am installing an HDX800 with SV-261 transponder in my ancient RV4. I am keeping my old Rochester piper engine gauges, so I am not relying on SV for engine instrumentation and specifically oil pressure info on start up. The master switch and starter solenoid are difficult to access. For 34 years, I have switched all the avionics on after start up and off before shut down. I see the installation note to add diodes to the contactors. I would like to omit the diodes until I venture into the solenoid area when access will be easier. That may a year or so. In any event, I intend to continue my practice and to shut the HDX off before shut down and on after start up, so I see no risk of spiking it, precisely as I have with my avionics for these many years without any trouble. That said, the transponder has its own unswitched power supply cable that may or may not be affected by whether the HDX is off or on. I have two questions: does shutting off the HDX also shut off the transponder and isolate it from a start/stop spike? If not, is the transponder affected by a start/stop spike in any event? If the transponder is at risk, then I will switch the power supply to avoid a spike, but it would be easiest if the HDX power switch functioned as an avionics master at least for the transponder. Thanks in advance for your time and comment. John N95JF