What transducer for Northstar GPS

[EdwardEstabrook]

Hello,
I recently purchased my first 'proper' sailboat, a '73 Ericson 27.

I'm trying to get speed over water working.
* I have a Northstar 650 GPS which is not hooked up to a paddlewheel sensor
* I have a paddlewheel / temp combo sensor which is probably designed to work with a SiTex LCS 180 previously intalled in boat by a previous, previous owner.
* There is an LT8 connector leading from the existing paddle wheel / temp sensors to near the GPS unit which I could convert to an LT6 via a northstar-provided Y-cable (part number AA002429).
* Northstar said it's possible to break my GPS by connecting an incompatible transducer to it and suggested I purchase a new one 'just to be sure'.

Is this true?? I'd obviously prefer to plug in the existing transducer and see if it works rather than spend $150+ on a new one and pull my boat out of the water).

On the other hand, I certainly don't want to destroy a $1000 plus GPS and then still fork over for the 'right' transducer too.

How should I proceed?

1) Buy Y-cable and risk testing the existing transducer. I'd only want to do this with fairly high degree of certainty that I won't fry my GPS! (Note I looked at airmar's site and saw no reference to SiTex... any idea what transducers they use / how they're wired?). There is zero labeling or serial numbers visible on the transducer or wire itself. Total cost ~$40.

2) Buy new transducer and Y-cable and install. Total cost ~$200 + boat haulout.

Thanks for the suggestions,
Ed