Harness Ground problem

I purt a new dash harness in my '72. Everything went in and hooke dup fine, but I'm guessing I have a bad ground. When I turn on the headlamps the "Bright" lights up even though their on low beam, and the instrument bilbs in the speedo don't light up. Everything else is OK. Anyone got an idea to try? I'm pretty sure the ground by the drivers door post is good. Could the ground around the headlamp switch be the problem?