Light switch relay

I'm going to be installing a new fuse block. I'm cheap, but classy, and the fuse block I picked up is not oem style. It's has a (+) bus, with the separate circuits branching off. This creates a problem with keyed hot vs constant hot. Easy enough to use relays for keyed hot and use original trigger source to close the relays. That won't work with the dimmer function.

What I'm thinking is to put in a relay to the light switch, triggered off of a keyed source. Key off, no lights. Extra points for not leaving my lights on and killing the battery. The accessory lights line will no longer have a dedicated fuse. Instead, it will be the entire light switch that's fused. My question is, is there any reason for this to be a bad idea? The headlights will be on their own relays under the hood, so minimal power draw through the switch lines.

This will be the new fuse block: Summit Racing® Fuse Blocks SUM-900357

The brake lights, dome, and hazards ((if your car has them) are also usually constantly hot. If you need your hazards on and be away from the car, you'll have to leave the keys. You might miss the interior lights.
What's wrong w the old one?
Evans Wiring has original fuse blocks at one time. You might have to call and ask about it

I am in the process of doing a complete rewriting on my 47 Dodge. I found a fuse block at Del City that has 2 separate busses that I will use one for hot all the time and the other for hot only when the ignition is in the run or ACC position. Each side has provisions for up to 10 fuses and a plus - Made in the US!

A couple of reasons, the first is to get rid of glass fuses. No hazards, so that's not a concern. The second is one side of one of the fuses is missing and another fuse is wrapped in foil. Since I have to tear into it anyway and ensure wires aren't fubar, I might as well upgrade.

But, you're right. I'll have to go back over the diagrams to double check the dome lighting. If they do go through the light switch, I may have to skip the relay idea. Or wire the dome lights as secondary stand alone circuit.

Headlight switch has 2 power supplies B1 and B2 for a reason. with only 1, a short at at tag lamp, trailer harness, anywhere, takes out ALL exterior lighting. So... separate circuits. Smaller fixtures and wiring fuse protected. Headlamps on a cycling circuit breaker.
headlight relays pretty much render the cycling circuit breaker in the headlight switch worthless so each circuit should have fuse. Short would stop, high beams or low beams but not both.
You could fuse B1 and B2 but keep those separate, not together on 1 fuse.

I need to ohm out the light switch. It looks like the dome lights always have power, and the light switch and door switches simply ground them out.

Redfish, B2 looks to power auxiliary lights, with an extra tap for brake lights. The way I'm reading the drawing, the stop light switch has redundant power feeds. One straight from B2, another fused from the "welded" link.

Nevermind. I was going to reconfigure more lines to dedicated fuse circuits, but this is too much work to make a key off lights off circuit.

Be careful what you wish for. You can easily create a "single point of failure" that might not be fun at say, 80 mph on a dark night. (Isn't the term dark night an oxymoron?) ANYWAY.............

It's a single point of failure as it is, with a higher probability wired orm style. Headlight relays alleviate almost all of the risk. The extra stuff I'm thinking of doesn't change any risk, just changes where the failure would occur. 50 year old light switch, or new fuse block.

However, it's a lot of extra work for no tangible benefit. So, new fuse block with the switch fused instead of fuses post switch.