Some proposals are titled "Contract Proposal", which would be a little more clear. You are proposing to work for payment, and when they sign they are agreeing to it.
As you're new to this be very careful how you write your proposal. I'd avoid phrases like "wire your house". Be very specific in what you're installing where, and in what quantities. I write out quantities (five) so a 5 can't be turned into a 15 or 25. I should have a sticker to put on proposals that says something like, "Unless specifically written, repair or replacement of non-professional wiring is NOT part of this contract. You never know what you'll run into.