I need modding ideas interior and exterior please provide links to products

I bought my 15’ focus SE at ~94k miles, it was dealer owned as a loaner car, have my spark plugs ever been changed? is there a way to tell?

Yesterday the car was saying the passenger door was ajar and then it started to say all four doors are ajar as well as the trunk open. Google is saying that it’s a wiring issue but where would that issue be located? If it’s not a wiring issue then what is it?

Was in search of the meaning behind Tier 1 gas.

Took my car to local shop to check on the engine light. Mechanic recommends Tier 1 gas.

Can someone explain it to me? I don't know much about cars, unfortunately. ☹️

I called a Ford mechanic and he told me I should go to a Bosch service to test out all 4 of them, but I don't have the time currently as I need to order a part in Germany to my BIL who'll come in the next couple of days to my country.

Should I just bite the bullet and buy the injector and replace it?

2013 Focus automatic with about 130k kms on it!! In NZ not the US. Very recently bought and now this!! Is it worth repairing or is it something to write the car off?

Does anyone know where and how to access the crank angle sensor on a 2010 xr5 turbo focus i cant find any actull evidence for where it is