Hi,
Mine's a DHC and I use the HRW part of the loom for something else. It was simple enough to fit a switch in the original place.
If the ignition switch is off, it's deactivated. If the ignition switch is on, it receives power whether the engine is running or not.
I find it's the same for the seat belt sign.
Adam
TR7 V8 DHC Jaguar Solent Blue. 9.35cr Range Rover V8, Holley 390cfm, JWR Dual Port, 214 Cam, Lumention, Tubular Manifolds, Single Pipe Exh, 3.08 Rear, 200lb Spax & PolyBushes, Anti- Dive, Capri Vented Discs & Calipers, Braided Hoses, 4 Speed Rear Cylinders, Uprated Master Cylinder & Servo, AT 5 Spokes and Cruise Lights. No Door Stickers. Mine since July 1986, V8 from 1991