I’d be cautious with that. It should be ok, but if the relay suddenly went bad you could end up with the ignition sense lead grounded while the radio is powered up. Ignition sense is looking for presence or absence of 12v, not ground.
That’s definitely worst case complete catastrophic failure of a relay like I’ve never seen! I suppose it is technically possible to have the drain side of the coil short to a working relay contact, but I’d bet on the entire vehicle catching on fire or wires just melting together before that would happen. A single pole single throw relay is pretty robust!
On a Harris remote head install, you always use the ign sense on the control head and leave the ign sense on the brick unconnected. I think you have a supply problem. Either something isn’t well grounded, or ign sense power isn’t stable. If the source voltage used for sensing (fuse tap), whether direct or switching a relay isn’t stable, neither method will work as expected.
Does the radio function perfectly up and to the point that the key is turned off? It doesn’t fail at some point during the drive? If this is absolutely the case, check to make sure there isn’t a delay power down on the circuit your fuse tap is connected to. Many new vehicles have a ton of circuits that power on with the key, but when you turn the key off, they will stay on until you open the door or for a set period of time.
I would make sure that the circuit you have chosen to tap is indeed turning off cleanly with the key and doesn’t blip off and then quickly reapply power on a delay circuit. A digital multimeter may not catch such a quick blip but a circuit test light would let you see a blip. Alternately, you could try opening the door before you turn the key off. That should ensure that the circuits will stay off when the key is turned off. Lastly, be sure to use a circuit that doesn’t switch with accessory mode. Many new cars use a key switch where accessory mode is forward one click, ign is two clicks, and start is mom forward from there. This means that when the engine is turned off, it actually passes the acc position before the key can come out.
Just some stuff to think about.
-B