If I'm not mistaken, the DMM should read 1.8ohms at the amps speaker output. As for polarity, + to + and - to -. Make sure the power lead from the battery is on the + terminal of the amp and not on the - (ground) terminal.
"Acoustics is the study of sound; a branch of physics dealing with sound. The law of physics is constantly challenge. Therefore in relation to acoustics; You must study constantly, for you will be constantly challenged." ...... Rainmanspl