Why is a 5- or 10-amp-fused control circuit any different than a 5- or 10-amp-fused lighting circuit?
That's the thing. The control circuit should be fused at the half amp, or 1amp level. Nobody's discussed that. But it's also not really useful in this case. You don't wanna be running 22 or 30 ga wires to the switch, just for durability reasons, and if you're stringing 16ga.. and you don't wanna tie it into other logic, might as well carry the load on it.
Sorry to stir up so much controversy, I get bitchy about the time someone has spent as a whatever. I know 6 month mechanics that as good as anybody.
I have only spent 34 years as a heavy duty and automotive mechanic so you probably know more about electrical failures in automotive than me
Your emphasis on "I've done this a long time" is a crutch. It's clear you know your stuff (knowing duetch standard pin numbers off the top of your head says something) Your accusation of "6 month mechanics" is also pretty nice. You're also using it to attempt to stop other conversation. Your appeal to expertise (as much as you might have) is not well founded in this case. It's clear you're aware it's bitchy, then maybe.. don't. You also discount the 40 year mechanics who can't wrap a wire harness, or won't touch an engine with variable valve timing.
The history of the pin numbers is fun too. The pin numbers come from the germans deciding everything needed the to be labeled "the same". It's useful!. But also not relevant here. I'm glad you know how to use a relay. We all ~should~. Honestly, given the loads here, using an automotive relay is silly, it's bigger, uglier, and unless you get a good, actually weathersealed one, not any better than a PCB mount version. Larry asked "why". The reason you'd use a relay in this case, is to enable relay logic, and to tie it into ~some other system~. Relays are another point of failure, cost more, and take up more space. For 1.6amps? Even OEM's don't use relays.
I'm going to give you the benifit of the doubt here. Since you've been doing this for so long, I assume you're accustomed to foglights, and driving lights, taking ~several amps~ per lamp. With the LED revolution, that's just not true anymore. 10-15 years ago, a driving light setup will be pulling a minimum of 8amps, and likely as much as 16. I'd be exactly with you here. If you wanna hear a fun one? The LED headlights on my Cherokee, due to how the grounding works on the car, will stay turned on if I don't turn them off before shutting off the engine. The relay is self energizing because of where the relay is grounded in reference to the headlight (I didn't do the install...) but that's ~another~ reason why relays can be funny.
Lets be clear here, you're not "wrong." A relay is one way to do it. But direct wired switch is another, correct, way.