As per the manual:
Operational Modes
The HSI has four operational modes: INS/VOR Navigation (NAV), TACAN/VOR
Navigation (TAC), TACAN Offset Point/VOR Navigation (VAD) and Ground Controlled
Interception (TEL).
NAV (main INS/VOR navigation mode): In this mode, the HSI connects with the
INS and displays waypoint navigation information along with bearing to selected
VOR/ILS station. This is the only mode that allows to select between true or magnetic
headings, through its two sub modes:
Right now, if the airport where Im landing is not a waypoint and has no TACAN or VOR then there is no way to get DME anywhere; nor in the HUD or the HSI. The thin needle should point to the ILS station and provide DME as all ILS do but all it does is stay there and do nothing. The thin needle flag if off so it should work.