St. John's multi story is about as central as you can get, how secure, I honestly don't know, but probably as safe as you can get in any major city centre.
Sat nav is L1 1NQ. Says evening parking up to 15 hours £5, not sure when evening time starts nor ends.
Access is from Skelhorne street.
If your overly concerned about the security of your car, you can bang it up our path, but were about 7 miles from town center, and you'd have to factor in Taxi fares both ways, I couldn't drop you off unfortunately as I'm on nights.