For the Garmin GPS18x LVC, 5m  to the RTCM, the following works for me:
I have green on  6, yellow on 7, shield and 1-small black and large black on 8, white on 14, red on 13, 1-small black n/c. 
You need to do the diode calibration procedure and then set the levels.  
Hope this helps.
Chuck

On Thu, Nov 16, 2017 at 2:39 AM, Doug Kingston <dpk@randomnotes.org> wrote:
I can't get the RTCM to recognize the attached GPS unit.

I have determined that pin6 on the DB15 of the RTCM is transmit data to the GPS (using an oscilloscope) and that's hooked to the RxData line of the Garmin (green).  Will the Garmin respond if it does not have lock?

RTCM diagnostics complain:
Running Diagnostics...

Warning!! VF Diode NOT calibrated!!!

Testing PTT/External CTCSS
Error - Failed to read PTT/CTCSS in asserted state
Testing GPS UART
Error - Failed to read data from GPS UART

Any hints? or ways to get more diagnostics?

-Doug-