Hi fellow jag fans

I am in the final stages of converting my 85 XJS HE to manual transmission
and I need to pick someones brains on how to sort out a speedometer.

I have fitted a Getrag box out of a 3.6 (which I wouldn't recommend to the
faint hearted), and recognising early that this gearbox doesn't have a
speedo drive, I also fitted a 3.6 diff with a speedo pick up.  However, the
pick up on the diff has 3 wires, whaereas my car has only 2.  I read on the
web (a book which someone in the US has put together on the XJS) that all
later XJSs were fitted with a diff pick up, but an interface module is
required because the later pick ups produce the wrong sort of signal for the
speedo, computer and cruise control

If I get hold of an interface module out of a late XJS, will it put out a
signal which my car can use, or do I have to change the speedo, computer and
cruise unit?

Steve Shuttleworth