I just bought a used Autometer Water temp and want to hook it up. I has the sender (27) but no instructions. Do I replace the sender that is in there now with this one and have a "dead" factory gauge, or how do you guys do this?

Take out the OE sender and put the autometer in it's place. All you need is an open end wrench and connector to hook up the sending wire. Thats it. Not hard at all. Oh yaeh! You need to wrap the threads of the sender with teflon tape or whatever.
Hope this helps.

So I'm gonna figure that the one in the cluster won't work anymore.

what i did was take out the old sending unit (dont throw it away) and go to the hard ware store and get some brass "T" fittings and hook them both up, dont forget teh teflon tape!!!!!!! And both of my gauges (in dash and aux. temp gauge) work like a charm.

both senders? I don't follow. Saturday is my brain's day off. Got a pic? Sounds like what I would want but, I want to catch on to what you did before I take more shit apart. Thanks!