I was reading your web review of the Raymarine ST2000 tiller pilot which I use. You list a "pro" as being able to use an external compass, but I have seen information on the Raymarine website that the tiller pilots won't override their internal compass. I would like to confirm if you have tested this successfully or have a definitive source. The ultimate solution is to upgrade to one of the new EV-1 or EV-2 systems with a tiller pilot but it is a bit out of my price range right now so looking to find a lower cost solution.
Although we have not professionally done this, we spoke to Raymarine and they confirmed the following:
In order for your ST2000+ tiller autopilot to receive and external compass, you must install an ST40 or ST60 dedicated compass instrument which terminates both a SeaTalk connection and also the 4 wires from an external compass. This ST40 or ST60 instrument will bridge the external compass info on SeaTalk and the ST2000+ will "listen" to the external versus internal compass.