I do not know the answer but I have a Yeoman and when I telephoned them with a similar query they were very helpful. They also have a web site which might reveal the answer to your question.
I can't see your Navman listed but if you go to <A target="_blank" HREF=http://www.yeomanuk.co.uk/tech/hometech.htm>http://www.yeomanuk.co.uk/tech/hometech.htm</A> you can look at some of these to finde what connection do what and then relate these to the Navman manual if it gives you the inputs and outputs.