Map F5 as a backspace

System Preferences>Keyboard>Keyboard Shortcuts.

I'm not sure I even understand the question; all keyboards here have backspace (which is also back delete) directly above the return key. No use of Fn key required.

What keyboard are you using?

By backspace, do you mean moving the cursor back along the line without deleting? If so, that's what the arrow keys are for.

And no; I can't figure out how to map F5 to that either.

Well, it's a while now since I used a PC (only ever used at work) but all the keyboards I used there had the same functionality as this one; backspace (=back delete) and delete (=forward delete). The key board on my Macbook lacks the delete key, but the backspace provides forward delete with Fn+backspace.

OK; just done a trawl on the Apple store, and I see now what you're getting at. The US bluetooth keyboard does indeed have delete in place of the backspace. I can't for the life of me think why, but there we are!

As for the original question, sorry I haven't been able to suss that one myself.

You're welcome. Hope someone can come up with an answer for you.

On every Mac I've ever used, the key marked "delete", sitting to the right of = and above \, performs the backspace function. If yours is working differently, then something is misconfigured. Or your keyboard is defective. You need to figure that out rather than try to work around it by mapping a function key.

The most likely cause is your keyboard layout setting is incorrect. Go to System Preferences -> Language & Text -> Input Sources, select U.S., and make sure nothing else is selected. See if that changes anything. If not, try creating a new user account, and see if that account has the same problem.