DCC - effect on old Farish loco's

Hi noelp and welcome
I have converted several old farish locos to dcc. However if you're unsure what to do you might want to think twice. A search here will help.
You haven't said if They are steam or diesel and also what era from farish? Steam locos can be converted with the use of a dcc supplies digihat. Search the dccsupplies website. I believe Poole diesels require 2 digihats but I haven't tried this.
Whatever you are doing, dcc will not make poor running dc locos run well. So if you don't have 5 pole motors in your locos I would forget it. In fact in most cases I would forget for a couple of reasons. If for instance you have an old black 5, consider seriously buying a new version black five. The detail is superior and the conversion to dcc is simple, a plug in decoder, twenty second job, as opposed to converting an old version which is visually inferior and will probably take a couple of hours to convert.
As to functions on decoders, in n gauge it's not really an issue in British locos. All 6 pin plug in decoders allow lights and motor functions, which is about all we can fit in. Steam thingies and dcc operated uncoupling is for the 2 mill people I think hope this helps

Hi noelp
You should be fine if you use 5 pole motors.

As pointed out above, it's not that difficult and with careful examination of the chassis you can convert the locos. Just check and double check that the motor is isolated from the chassis. If it's not, you've lost a decoder. For this reason you might want to look at decoders with goof proof warranties such as TCS or Lenz, but of course these are more expensive than the digitrax suggested.
In steam locos you will almost certainly only need to use four wires from a decoder, 2 to the pickups, and 2 to the motor. You won't need lights on old farish steamers, and therefore all the wires except red black grey and orange can be cut off, unless you plan to reuse the decoder elsewhere. Good luck and let us know how you get on.
HTH Cheers.
kirky