If a host of a multiplayer game were to insert a fault into the scenario via the F11 screen, would the player whos panel is affected get an indication that the fault has occurred in the same way as for a computer-generated fault?

Also, is there a diagram anywhere, of exactly which track circuits, points and signals are where on the ground? Signals can of course be found out easily, but tracks and points cannot.

No, you don't get any special indication.
As for the track circuit and points locations, you can use that mouse symbol button to find out which designation belongs to which piece of track.

no the player does not get any info saying that a fault has occured or when its fixed
as to the locating of track circuit and points, there a button that has a mouse on it. this button when pressed allows you to click on the relavent track circuit, signal or points which will then bring it up in the list for you.
for further infor look at this
www.simsig.co.uk/dokuwiki/doku.php?id=usertrack:ssrun:func:f11

So in reality if the host plays those sort of "games" its more like reality than the computer telling you something has failed.

Thanks for the advice about the mouse icon, never knew about that.