Aaah.. Copied the installed, add-on version to my hangar and ran. Radar didn't work. Deleted HUD file and substituted HUD file from earlier version. Now radar works, as do all other parts of upgraded version. So, radar problem
with upgraded version resides in its HUD file, which may be corrupted. Comparing HUD file between new and old version, but still haven't found any bug. Nevertheless, this is progress, and am glad to have fully working upgraded version in my hangar.
P.S Printed out both Hud files, compared line by line, and found them identical; so am mystified why radar works using one, but not the other.