bird_dog

If you want to go that route I'm thinking you will need to buy some wheels that are the same size as the ones on the front. The tires on the rear are much wider than the ones on the front. I don't think the smaller tires could be mounted on the wide wheels.

The only other brand I looked at was Pirelli and they were the same: "For vehicles equipped with staggered size fitments (different tire sizes front and rear), the mileage warranty for the rear tires will be 50% of the stated mileage warranty for that line. Run Flat tires will have a mileage warranty of 50% of the stated mileage warranty for that line, not to exceed 30,000 miles, whichever is lower." Just look under "Milage Warranty" for whatever brand you are looking at buying.

Since nobody else has responded...I used to work as a mechanic but only on domestic cars and trucks. I have absolutely no work experience on the Lexus. It sounds like you might have a short that is feeding back through your ignition switch. I would probably start by disconnecting the wiring harness from the ignition switch and trying to identify a wire in that plug which is hot when it's not supposed to be. You would need a wiring diagram or compare the wires to another vehicle to figure out which ones are normally hot with the ignition off. If you don't have access to one or the other I might try unplugging the harness feeding the steering column or just start pulling those relays under the hood (one at a time) to see if one of them turns everything off. Some of the items you list are controlled through the steering column wiring harness but others I wouldn't think are.

I just bought a used IS250 and I'm looking for some tires also. I don't want to pop anybodys bubble but I think if you read the fine print on the Michelin tires you will find the warranty is half of 45,000 miles (or whatever your milage rating is) if they are different size tires on the front and rear as mine are. They can't be rotated so they reduce the wear warranty by half. It's still the same tire so it really should not make any difference unless you are burning rubber off the rear tires. I haven't checked any of the other manufacturers yet but I would imagine they probably have about the same policy.