Brian (b) I also note that my UHF radio is wired into a permanent power source - possibly to do with it being bad for the UHF unit to have it continually switched on and off with the ign.
You mentioned the PO had fitted, then removed a UHF unit.

It could be worth seeing if a cut wire around where the UHF unit was has grouned - and close up the ends of any cut wires you find.