I have the factory installed depth guage, Lowrance LST-3800.It has the option to read water temp, of course being factory they take the shortcut/cheapness of not adding all features. The question is, is this just a plug and play feature such as adding this sensor 106-69? It is mid way down on the right side of this link page. http://www.lei-extras.com/store/search.asp?SearchType=Category&Category=200+khz+transducer
The 106-69 is a shoot through hull transducer, which im assuming you probably do have. A lot of the skimmer type transducers that are mounted on the transom's have the temp sensor built in. You will need to mount the remote temp sensor included with the xducer probably on the transom or somewhere that is underwater. Data Sheet According to the lowrance website the gauge you have does have a terminal on the back for connecting the temp sensor so it should be as easy as mounting the temp sensor and hooking it up to the gauge.
if you scroll down the page a little there is a diagram of the connector of the depth gauge, I would make sure yours matches and that nothing is already connected to the temp1 temp1ground pins. (the wiring may connect at the transducer!)
Thanks PT, I was hoping it would be that easy, I'm not in a rush now since the water is warm. Since I have the extra time I'll call the 800 and make sure I order what I need. GW