This mostly applies to vehicles.
Under the construction rules for Heavy Gauss Rifles, the carrying unit is required to be powered by a fusion or fission engine (p. 218-219 in my older TM, but no errata has changed it).
Total Warfare lists the HGR as having types DB, X and V, all of which make sense (TW table p.303).
The issue comes up with vehicles mounting HGRs. The engine hit critical effect (TW p. 195) does nothing to stop an HGR from operating once the vehicle's engine is destroyed.
Engine Hit: The vehicle’s engine is severely damaged. The vehicle may not move or change facing for the remainder of the game and is considered an immobile target. However, its electronics still function; any Direct-Fire Energy and Pulse Weapons no longer work; also treat as a turret lock.
On a side note, when did gauss rifles stop requiring power amplifiers during construction of non-fusion/fission engined units? And, is it intentional for all gauss weapons to continue operating with an engine destroyed? (The interaction of power amplifiers shutting down with the engine would have stopped gauss weapons from working without a functional engine.)
